Stats:
~10 Vigor
~10 Endurance
5 Vitality (base)
25 Attunement
7 Strength
7 Dexterity (base)
8 Adaptability (base)
50 Intelligence (we'll be using gear which increases this stat)
4 Faith (base)

The equipment we'll use at the end of this guide:
Magic Staff of Wisdom +4
Lightning Foot Soldier's Sword +10 (any element goes, but Lightning is overall very good and Magic, while apparently being the first choice, doesn't add much AR at all)

Warlock Mask/Hexer's Hood
Lion Mage Robe
Lion Mage Cuffs
Lion Mage Skirt

Southern Ritual Band +2
Clear Bluestone Ring +2
Chloranthy Ring +1
Second Dragon Ring

This gives us
- some survivability and stamina
- the ability to use our sidearm-weapon of choice and some shields
- good spell-damage and access to the best PvE-Sorcery-Staff
- lots of casts to work with and
- good casting speed
And all of that at around SL70-75.

If you have troubles as in you're dying too much you should put a couple of levels into Vigor. It increases your survivability by a lot and even caster-type builds should have a decent chunk in the endgame.

Starting Class: Sorcerer
Starting Gift: Bonfire Ascetic

First off: Pick up any not mentioned Titanite Shards, Large Shards and Chunks from copses or Crystal Lizards, you can later use it to upgrade armor and shields. However, do not buy more than necessary and do not upgrade any armor or shield until you've obtained the mentioned gear, maxed out your weapon and your staff and met the requirements to use the staff of choice - you will need the souls to level up for sure!

Grab the Small Smooth & Silky Stone just in front of the character-creation house.
Inside that house, create your character (hint: heroines should be preferred as lots of casting-dedicated gear looks better on females), grab the Effigy.
Trade the Stone with Dyna and Tillo (aka the crownest) in the Things Betwixt and pray that you get something useful like infusion-stones or upgrade-materials.

Pick up the Binoculars (and the Divine Blessing, never hurts to have one) when you enter Majula. You probably won't need them, but they can be used to snipe foes with your spells.

The other notable loot in Majula (Homeward Bones, Titanite Shard, Estus Shard) is worth picking up, too.
Join the Way of the Blue, their ring is nice to have early on and in case that you get invaded you may receive a helping hand.

Start with Heide's Tower. Grab the Crimson Parma in your way. Cheese the Dragonrider ("6-step-method"). Talk to Licia and exhaust her dialogue.

Next: The Forest of Fallen Giants!
Optional, but recommended: Grab the Rusted Coin on the way Majula -> FoFG, it'll help you with the little farm you've to do in a few minutes.
Skip everything, just go for the second bonfire "Cardinal Tower". Talk to the merchant Hag Melentia until her dialogue is exhausted. Buy Lenigrast's Key, another scroll of Soul Arrow and a Firebomb (if you didn't get one as a random drop before).
Kill the Crystal Lizard upstairs and pick up its 2 Titanite Shards.
Farm a Foot Soldier's Sword from the Hollow Infantries wielding it (the sword'n'board ones, i.e. just outside of the bonfire-room - drop down and fight them)

Optional: Pick up the Small White Sign Soapstone and the Small Leather Shield.

Buy a Firebomb and blow up the wall to the first Pursuer-encounter. In case you don't know how that works: This is the spot you've to stand at:
Now throw the Firebomb and the wall blows up. Remember that it'll damage you, so don't do that at low health.

Optional: Run further, do Pate's White Sign Soapstone quest and pick up the Large Leather Shield. Unlock the shortcut to the Last Giant. You can kill the Last Giant for the souls, but it isn't mandatory. I'd recommend it, he needs about 25 Soul Arrows to die.

Teleport to Majula. Consume the Dragonrider's Soul and other souls you may have obtained.
Access Lenigrast's store. Buy as many Titanite Shards as you need to have 12 in total. Upgrade both your Sorcerer's Staff and Foot Soldier's Sword to +3.
Level up with the remaining levels - level Strength to 7, Attunement to at least 16 (attune the recently found Soul Arrow and Great Soul Arrow) and split the remaining level into Attunement and Intelligence. Tip: Don't level Attunement above 25 till lategame, base Adaptability and 24 Attunement already give you 92 Agility which is a useful breakpoint for iframes during rolls!
I didn't have much luck farming for the sword so I got a few thousand souls from farming hollows, I had to buy 9 Titanite Shards and could level Intelligence to 19 without using any of the consumable souls.
Keep 2,000 souls to be able to pay Licia to open the path to the Huntsman's Copse!

Next: Walk towards the Heide's Tower entrance, talk to Licia and pay her 2,000 souls to open the path to the Huntsman's Copse.
Run through there, light the first bonfire.

Optional: Kill Felkin, he'll drop the Sunset Staff and more importantly, you can buy his Hexer's Hood from Hag Melentia in Majula.

Keep running and light the second bonfire.
Now drop down to where all the poisionous butterflies are at. Kill the Giant Basilisk at the bottom. He'll drop 3 Large Titanite Shards. Return to the bonfire and repeat this 3 times so that you have at least 12 Large Titanite Shards.
The butterflies drop Poison Moss which is quite useful, too, so make sure to grab some.
Warp back to Majula and reinforce both the Sorcerer's Staff and Foot Soldier's Sword to +6. You should have enough souls from killing the enemies here.

Now teleport to the second bonfire in Heide's Tower to visit the No Man's Wharf. On your way down make sure to grab the Sublime Bone Dust.
Skip the enemies at the start and run to ring the bell at the top. On the way back grab the Fragrant Branch of Yore. Talk to the Sorcery-merchant Carhillion of the Fold. Because I had some consumable souls to spare, I consumed them and bought all Great Soul Arrow, Heavy Soul Arrow (you don't have to buy this), Great Heavy Soul Arrow and Yearn. The latter spell is VERY useful, make sure to get it!
Unlock the bridge-shortcut, go back to the bonfire and teleport to the second bonfire in the Huntsman's Copse.

Proceed towards the level to lower the bridge and kill the enemies on your way. Don't forget about the Syan Knight guarding Soul Spear and another Sublime Bone Dust!
I strongly recommend you to kill the enemies BEFORE pulling the lever.
Since the third bonfire isn't accessible yet, continue the path over the bridge. Kill the enemies. The goal is to grab the Undead Lockaway Key to open the bonfire-room. There's an NPC-invader, Merciless Roenna, but she's fairly weak.
Pick up the key, backtrack and open the door to the bonfire. Light it and talk to Creighton (because why not). Warp back to Majula.
Tip: Burn the 2 Sublime Bone Dusts! Level up with the remaining souls.

With the reinforced gear tackle the next path, the Shaded Woods. There's a room with the petrified Rosabeth of Melfia. Use the Branch of Yore and unpetrify her!

Optional: Talk to her, gift her some random gear and talk to Benhart!

Before pulling the lever, kill the enemies on the ground-floor. Now pull the level and kill the enemies who're dropping down from above. Don't forget that there's a Basilisk, too, when the gate is opened. It's a bit tricky, but they should die with 2 casts of Great Soul Arrow.
Light the bonfire (don't rest!) behind a door in the next room, grab the Estus Shard on the other side and keep going. Just skip all the enemies and light the second bonfire.

Optional: Kill the Falconers at the start of the left path (5 to be exact) and grab the loot of the copse behind that aquaduct (Human Effigy, 2x Twinkling Titanite and a soul).

Walk through the gate to the right and enter the foggy part of the Shaded Woods. Hug the left wall until you meet Vengarl. Sometimes one invisible enemy will follow you, take care of him if neccessary. Use the sword, they're extremely hard to kill with spells. Now keep hugging the left wall. You'll soon get out of there and find the third bonfire. Light it, then look here
Make sure that you have at least 1 Homewardbone! Jump down on the little bridge. Kill the Syan Knight and grab another Sublime Bone Dusk! Walk back to that little bridge, jump over the little gap seen here
open the chest and loot the Black Knight Halberd! It has no use as a weapon for you, but you may appreciate this weapon later in case you're out of Firebombs. You have to use a Homewardbone to get back.
Backtrack to the foggy area, hug the left wall. You'll see a chest above your head at some point. It contains the Chloranthy Ring +1. Keep hugging the wall until you can walk up the ramp leading to the chest. There's at least one invisible dude, so hurry and sprint! Open the chest, grab the ring, jump down and sprint back to the bonfire. Equip the ring.

I warped back and spent my souls to level up, by now I had 25 Attunement and 20 Intelligence.

Next, keep going further. Once you're in the open area, turn 180° and do a little jump here
to loot the chest with the Titanite Chunk. The invisible dude there likes to break it, so loot the chest first and then deal with him.
Tackle the boss. Najka is pretty predictable, just stay in her front, shield up, and wait for her to either do the grab or the twin-sting-thrust. One spell each time, slowly wear her down.
Once she's defeated, light the next bonfire in the Doors of Pharros. Warp back to Majula and buy the Ring of Whisper and the Silvercat Ring. Use the remaining souls to level up and don't forget to burn the Sublime Bone Dusk.
Warp back the the third Shaded Woods bonfire. Equip the Ring of Whispers. Go to Manscorpion Tark, talk to him and you'll receive another Fragrant Branch of Yore. Kill the Crystal Lizard there.

Optional: Kill him, he drops the Second Dragon Ring. Equip it! Otherwise he'll give it to you after you've killed Freja.

Now use the Branch to unpetrify the Lion Warrior near the bonfire. Jump on the other side, there's a couple of ways to do that. Kill him - Lion Warriors are extremely resistant to any element, so use your sword, they're also very easy to backstab and have infinite Poise. He drops the Fang Key.
Use the Fang Key to free Ornifex in the pit there. Grab the Branch next to her. Grab the Twinkling Titanite next to her room.
Use the new Branch to obtain the Lion Mage Set. Equip it! You'll receive yet another Branch on top.
Use that Branch to unpetrify the Lion Warrior holding the Warlock Mask next to the Golden Lion Warrior (he's a bit tougher than the usual ones). Equip it, too! It is very important that this is the last Lion Warrior you unpetrify! This use of a Branch will NOT give you another one!
Grab the Pharros Lockstone from a copse near these Lion Warriors.
That's it for this area for now! Warp back to Majula and spend your souls for levels. At this point I leveled Vigor and Endurance to 10 each and spent 1 or 2 points more for Intelligence.

Now warp to the Doors of Pharros.
Go into the big room next to the bonfire, kill the Mastodon and the rat and move on to the next room. Kill the 2 rats. Watch our for their Toxic-status. You should own some Poison Mosses though.
Climb the ladder, kill the 2 Gyrm Warriors and use a Pharros Lockstone here:

Hop down, enter the newly opened path. Loot the chest and obtain a Twinkling Titanite and a Faintstone.
Go upstairs again, follow the path, loot the next chest (warning, there's another Gyrm Warrior desperate to destroy it!) for the Titanite Chunk and move on to the next bonfire.
Warp back to the first bonfire in the Doors of Pharros. Now take the other path and sprint through the area. Light the bonfire in the Brightstonecove Tseldora!
Now hug the left. The Falconers are brutal. This is the way to face the least of them.
Use the Binoculars if you have them. Snipe the archer-one on the tower. Watch out, a melee one likes to notice you and to stab your back. Go to the left of a destroyed building. In that building the Staff of Wisdom is held by a Mimic! However, it's impossible to enter it now.
Snipe the next archer. Now snipe the roof of the water well. It'll break after ~5 spells.
The next part is tricky. Jump from the ramp and into that well. You may need a few tries. The pigs and the remaining archer can be annoying, but just ignore them.
Once you've done the jump, watch out for the pig in there. You can stunlock it with your sword.
Climb the ladder, kill the Mimic (watch out for the archer!) and loot the Staff of Wisdom! Now warp back or go outside and run for your life, back to the bonfire.

Now it's time to nuke the Pursuer. Warp to the Forest of Fallen Giants, second bonfire. Walk through the blown up wall, up the platform and wait for the Pursuer to drop down. Kill him, shouldn't be very hard by now. Don't forget to loot the Estus Shard and don't forget that the seemingly dead hollows will now be aggro.

Next is the actual Pursuer's bossroom. Walk through it like a boss. Interact with the nest. Don't ever stop for the Drangleic Set, it's for nubs and we don't need it, right?!
Get grabbed and land in the Lost Bastille. Loot the chests, the important one is the one with the Dull Ember. Light the bonfire, go outside, tackle the next Pursuer and loot the Twinkling Titanite he drops. Loot the chest because another Branch is always nice to have. Proceed, talk to Lucatiel, loot the Antiquated Key (even though you don't really need it for this run), bait the mummy "guarding" the explosive barrel in front of the stairs to go back (we need that barrel alive!). Kill it. Sprint towards the barrel and sprint downstairs, "pushing" the barrel. It should blow up the wall with the big crack. If not, throw anything fiery at it or shoot or attack it with a fire-element weapon, like the Black Knight Halberd we picked up previously. Kill the dogs first (old Dark Souls truism). Light the bonfire, light a Torch at the bonfire and light the scone in the blacksmith's shop. Rest at the bonfire, talk to McDuff, give him the Dull Ember and infuse your Foot Soldier's Sword with Lightning and your Staff of Wisdom with Magic. Loot the metal chest he sat on previously, Twinkling Titanite is important!

Warp back to Majula and level up, hand over any Estus Shards you have picked up, burn any Sublime Bone Dusts you forgot to burn previously and upgrade the Foot Soldier's Sword as much as possible. Do not upgrade the Sorcerer's Staff!
I pumped Intelligence, I had around 30 at this point and after consuming most of my non-boss souls (I consumed no boss soul except the Last Giant's and the Dragonrider's). I also bought and equipped the Hexer's Hood instead of the Warlock Mask.

At some point in this part of the playthrough I tackled the Skeleton Lords. It doesn't really matter when you do it, but not later than now is a good time. Warp to the third bonfire in the Huntsman's Copse. Make sure to have Yearn attuned. Skip all the Rogues to save spells and weapon-durability.
Enter the bossfight and complete it. I like to start with the caster, kill him, lure the other 2 Lords away and 2 Bonewheel Skeletons spawn. Kill them when they spawn, one Great Heavy Soul Arrow should be enough. Then it's up to you which one to kill next, it doesn't really matter. Cast Yearn when the crowd spawns and kill the Skeletons while they're distracted. You probably need 2 or 3 casts of Yearn for each group of minions.
Finally all are dead and you can proceed. Lower the bridge, enter the Harvest Valley and light the first bonfire. Keep going and talk to Stonetrader Chloanne. Buy her Bonfire Ascetic and exhaust her dialogue.
In the first poison gas area there are 2 Titanite Chunks on (2 different) copses, loot them.
In the little cave there's another Fragrant Branch of Yore, never hurts to have another one.
Continue, open the big gate to gain access to the second part of the Harvest Valley and light the second bonfire. In the next poison gas pit there's a Titanite Slab! Pick it up, there's also a Simpleton's Spice you may want to take to spice down endgame-spells.
Return to the bonfire, warp to Majula, upgrade your sword if possible and level up with the remaining souls.

Warp to the third Shaded Woods bonfire, burn a Bonfire Ascetic.
Loot the chest with the Titanite Chunk.
Kill the Crystal Lizard where Manscorpion Tark is/used to be.
Grab the now 3x Twinkling Titanites in the pit where Ornifex used to be locked away.

Tip: You should now have enough upgrade-materials to upgrade the Lightning Foot Soldier's Sword to +10, so warp back to Majula and max it out!

Now kill Najka! It is a pretty tough fight, but be patient and chip her health away.
Congrats, after her death you'll obtain the Southern Ritual Band +2!

Warp back to Majula and level up.

Next are NG+ Skeleton Lords, so warp to the third bonfire in the Huntsman's Copse. FIRST, unlock the shortcur through the cave. Next to the shortcut-gate there's a Crystal Lizard and a copse with an Estus Shard, so make sure to get both.
Then burn a Bonfire Ascetic at the bonfire and take the shortcut-route through the cave. It's a lot less tedious like this. First focus on killing the Necromancers, maybe you get a lucky Lizard Staff drop, too! Next to the shortcut-gate there's a Crystal Lizard and a copse with an Estus Shard, so make sure to get both.

Kill the Skeleton Lords. The NPC-summon Creighton can be a good meatshield. Don't forget to use Yearn against the crowds.
After killing them you get the Clear Bluestone Ring +2!

Equip both new rings. Warp to Majula and level up.

After consuming all my souls but one Najka's Soul I could level Intelligence to 49, plus the Hexer's Hood giving me 50. In case that you keep using the Warlock Mask, you only need 48 Intelligence.
I also handed in the Estus Shard.
I had 9 Twinkling Titanites at this point and went straight to the blacksmith to upgrade the Magic Staff of Wisdom to +3.

In case that you're also able to wield the Staff of Wisdom, equip it!
You can now attune Soul Spear, too.

To grab all the Twinkling Titanite you need for one more reinforcement of the Staff of Wisdom do the optional parts of this guide that are related to Twinkling Titanite locations and make sure to have one Fragrant Branch of Yore in your inventory.
In case you picked up any tradable items such as (Small) Smooth & Silky Stones, trade them with the crownest (hint: you probably won't get any).
Unpetrify the hollow that blocks the path into one of the trees. Kick the tree, drop down and loot an Estus Shard. Kick down the tree to open a shortcut.
Nuke the two hippos and the now spawning Pursuer. He'll drop the last (in case you didn't have get a lucky trade before) Twinkling Titanite that you need to upgrade the Staff of Wisdom to +4!
Return to Majula and upgrade it! You can spend the rest of your souls for levels (Intelligence to whatever level you need to reach 50 with your gear - so 48 or 49 in case that you really didn't already meet the stats use the Staff of Wisdom), I'd recommend both Vigor and Endurance to 20 as a next step, or for upgrades of a shield or armor.

This is how I ended up:

Playtime around 4 1/2 hours, but you can do it way quicker than me. I died quite often, picked up "unneccessary" loot, needed some time to farm the Foot Soldier's Sword and went afk to add a quick note to this guide while playing.

Since the Staff of Wisdom isn't fully upgraded yet, you need 5 more Twinkling Titanite. But you have to actually progress some more to find more, so it's best do just clear the remaining game now!

You'll also have some lack of good spells. I played this far with only miscellaneous sorts of Soul Arrows and melee (the latter mostly in the Shaded Woods). You have one scroll of Soul Spear, but that isn't enough of the big-hitters.
You can trade the NG+-soul of Freja for Crystal Soul Spear.
You can do Navlaan's questline for Unleash Magic.

However, I recommend to you just progress normally for now - your staff is good enough and so is Great Heavy Soul Arrow. After you killed the Flexile Sentry in the No Man's Wharf (easy-peasy by now), Carhillion will move to Majula and after you opened the Shrine of Winter, he'll sell unlimited Great Heavy Soul Arrows so that's a good way of having a nice "clear-the-area"-stock.
Talk to him, he'll give you a Northern Ritual Band +1 once you have 30 or more Intelligence. It can be pretty useful for a glasscanon-caster!

Now, for the bosskill-spells: That's Soul Spear! Yes, Crystal Soul Spear is more damaging, but only deals 25% more damage. It costs 2 slots instead of 1 so the regular Soul Spears are a lot more efficient and still very strong.
You can farm them very easily by burning a Bonfire Ascetic at the second bonfire in the Huntsman's Copse. No need to kill any boss, just sprint to the Soul Spear copse, loot it and return or let yourself be killed. Repeat.

You can farm the Necromancers in the Executioner's Chariot bossfight for a Lizard Staff. It's basically the second-best Sorcery-Staff (or third, the Witchtree Branch is arguably more useful due to its speed). It's a bit less damaging than the Staff of Wisdom, but faster and has a lower casting height. It can also cast (Staff-)Hexes, so in case you want to use Dark Fog and co. it's good.

The next levels should be put into Attunement (to 50), Vigor (to 50), Adaptability (only 1 level to reach 99 Agility @50 Attunement), Endurance (to 20) - and then Strength and/or Dex for better weapons and shields of your choice. Lastly you can pump Endurance.

Other equipment I recommend for the lategame/higher NGs:

• Black Witch Domino Mask
  
• Blue Dagger
  
• Sorcery Clutch Ring
  
• Northern Ritual Band +2
  
• Third Dragon Ring
  
• Stone Ring

Thanks for reading this far, I hope the guide was helpful. Comments and constructive criticism are appreciated!