Control-Click for auto-loot.

Get the intelligence talent that lets you gather herbs first, then you can shift click every plant you pass when moving about to grab potion ingredients instantly.

Prioritize strength and stamina talents above all others, intelligence too if you use signs a lot.

It's probably not worth spending points on any of the signs aside from Aard and Igni

Get Aard sign stun upgrade early, most enemies in game are not stun-immune, even bosses, and you can kill a stunned enemy in single blow.

Also invest in group style, it awesomely reverses the situation when you're outnumbered(which is, to say, pretty much all the time) - the more enemies are next to you the harder it hits on all of them at once.

From there the simplest way to go is to just upgrade sword styles, try to have a few points in fast silver before the end of chapter 1 even though you don't have a silver sword yet, trust me on this. If you want to be more sign heavy Aard and Igni are great, but the others shouldn't be ignored.

Buy and read every book you can get your hands on. You need to learn about monsters and plants before you can harvest ingredients off of them, which you'll need to do for quests and potion-making.

When you use a blacksmith, you're not a actually upgrading your current sword, you're making a brand new one.

Don't be afraid to craft a meteorite sword as soon as you have any three stones, instead of waiting for a "good" combination. There's several unique swords scattered throughout the game that are generally better than anything you can craft at those points, so unless you rush through the main quest those meteorite pieces will quickly become vendor fodder.

Don't bother using any weapons aside from your swords. They really don't have a use beyond giving the enemies things to fight with.

Unlike other RPGs, potions aren't something you save and only drink before a tough fight. Ingredients are cheap and common for a reason - always have a few potions in your system, and drink more as appropriate.

If you make a potion with a special additional ingredient, make all future potions of that type with the same ingredient, otherwise they'll take up a separate inventory slot.

Use potions all the time, ingredients are plentiful, also try to brew potions with secondary effect for extra kick(same color ring around all ingredients).

It's worth adding health regeneration to long-lasting potions like Cat when exploring dungeons, or having lower toxicity on high-tox potions when buffing before a big fight.

Sell ingredients with chemical names(salts, acids, crystals etc) for money when you find some, brew potions from weeds and monster organs you collect, the difference in price is huge. Also grab all the vodkas you find for potion bases, buying it is too expensive and nobody minds you stealing the drinks from their home.

Perhaps more importantly, there is a very simple formula (which I think you learn in the prologue) to turn any strong alcohol into a top-tier potion base. Turn all the cheap booze you grab into White Gull and not only will that spare you from purchasing the expensive stuff, you will save a lot of inventory slots by only needing one stack for alchemy bases. Be careful that you don't use White Gull as a base for your White Gull alchemy though!

If you take long-lasting potions you can meditate to clear your toxicity while still keeping their effects active.

Make sure to learn how to make Specter Oil and have a jar of it handy before the end of Act 1.

Don't throw away unique ingredients. You'll get to make powerful potions with most boss monster body parts.

Also, keep at least one copy of every tooth / fang monster part.

Get anything you need out of storage at the beginning of Act V, because that's the only time you'll have access it for the entire act.

There's no need to buy The Tome of Fear and Loathing, because it can be acquired at the first Inn in a drinking contest.

Don't waste a skill point on Monster Lore, because it only gives bestiary/ingredient entries for Barghest, Ghoul, Graveir, and Drowner.