This guide also has a video version here if you'd prefer: https://youtu.be/gQCgfO6waXc
b]1.1 Races [/b]
In BG3, races are mostly the same, as you get to apply both a +2 and +1 to any two Stats of choice regardless of Race.
However, some still offer a few unique benefits.
Haflings get the very useful Lucky racial ability, which lets them reroll 1s once, for Attacks, Skills & even Saves.
Rolling a 1 is extremely annoying as it's a Critical Failure, no matter how high your modifier is, and due to how many checks/attacks you'll be doing as you play the game, some will definitely be Critical Misses and such.
Half-Orcs get two unique racials: Relentless Endurance to avoid Death once, and Savage Attacks for the highest potential Crit Damage in game, 3x instead of 2x.
Humans & Half-Elves have Civil Militia for Shield & Light Armor Proficiency, which can help Casters achieve higher AC.

1.2 Backgrounds
Usually you want a BG that complements your Character's Skills, by giving you Proficiency in other Skills you might find useful for your Build.
All Classes have some Skills they can choose to specialize in, and then you add the BG given ones to that! Such as having a Warlock proficient with History, Arcana, Deception & Stealth.

1.3 Stats
DEX is definitely the most stacked stat of them all, as it simply does way more than the rest.
First, it increases AC, although in BG3 Heavy Armor can also help characters with low DEX achieve great AC, it's not like in Pathfinder where the classic non armored "pajama" Tank is the way to go.
Second it increases BOTH To Hit Chance & Damage for Ranged & Fineassable Weapons.
In BG3, you don't need the Weapon Finesse feat for that, rather, Weapons that have the Finesse Tag like Daggers, Shortswords, Rapiers etc. automatically let you apply your DEX for such purposes.
This makes for a very versatile character, as you can have your DEX help when it comes to both Melee & Ranged, which also helps a lot with Stealth & High Ground as I'll explain later.
Third, it's the main source of increasing Initiative. As a Turn Based game, if your party members roll high on INI, they can all act BEFORE the enemies, which makes for very powerful Alpha Strikes.
Last but not least, DEX saving throws are the main way of avoiding a lot of Spell Damage like enemy Fireballs etc.
Also, due to the way BG3's Point Buy System works, you can easily achieve 16 DEX, 16-17 on your actual main Stat, and then 14 CON for nice HP regardless of Class/Race.
STR can be useful too, but mostly for 2H Builds and such, and for extra Jumping & Carrying Capacity.
CON is always nice for extra HP.
INT & CHA are rather dumpable for Classes that don't require them (almost everything but Wizard, Warlock, Sorc).
And as far as CHA for Dialogue Checks, you can always initiate them with a high CHA party member with Persuasion skills.

In BG3, there's 4 different type of Actions you can perform in battle, mostly limited to one of each type per Turn:

2.1 Movement
Thankfully, Movement is separate from other actions, so you can move as much as you want, modified by Race and other bonuses, and still retain the ability to perform all your other actions like Attacking & Casting Spells.

2.2 Main Action
This is usually the most common action type, used for Attacking, using Abilities & Casting Spells.
While you are limited to just one per turn, characters like the Martial Classes such as Fighter gain a second Attack at level 5, while Mages get double Cantrip power at the same level, so a Firebolt now dealts 2-20 instead of 1-10.

2.3 Bonus Action[/b]
Bonus Actions are great because they can be combined with a main action in the same Turn. Please be sure to check below the decription of whatever action you're going to perform to see if it's a Bonus Action or not.
For example, the Warlock Hex spell can be cast as a Bonus Action, which means you can combine it with your Eldritch Blast (Main Action) all in the same turn!
Drinking Potions is also Bonus, meaning a Fighter can attack the enemy and still quaff one to recover HP.
Some classes like Rogue even get to Dash & Hide as Bonus.
It stands to reason you'll ALWAYS want to combine at least a Main Action + Bonus Action in the same Turn for maximum efficiency.


2.4 Reactions
The last Action Type often comes during the enemy's turn.
For example, the Shield Spell can be cast as a Reaction, so that if the enemy's attack was about to hit you, you can use Shield to prevent that (even during their turn/attack)
War Clerics have Guiding Strike which can be used during your own Turn to highly increase your chances of hitting the enemy.
Items can also give you some, such as the Gloves of Missile Snaring to reduce ranged damage you might have received.

Stealth is to put it simply quite overpowered in BG3, and one of the easiest ways of handling battles even on Tactician.
Let's cover some of the main mechanics behind it:

3.1 Detection Zones
First, each enemy has a Cone of Vision coming from their front & outlined in Red, which is their Detection Zone.
Unless you are in brightly lit areas, you can use Stealth Checks to avoid detection even while standing in the Red Zones.
You can also press Shift out of Battle/Stealth to check that.
However, it's far better to avoid doing so and prepare an ambush outside the red areas instead.
Because enemies will patrol around the area, the Red Zones usually change depending on their position.
The easiest way to overcome that is to force Turn Based Mode once you find a good position, by either pressing SHIFT + SPACE, or clicking on the circle icon to the right.
This will freeze time even out of battle, which makes it vastly easier for your characters to move and ambush the enemy at will.

3.2 Entering Battle from Stealth
It's very important to realize that unless ALL your party members get detected from the initial stealth attack done by the first character, not everyone will join battle at once.
You can easily see what characters are currently in battle by checking the "Crossed Swords" icon to the Left of their portraits.
What this means is you can ALSO have your other characters that are still hidden perform their own attacks from Stealth to actually join battle from there onwards, one by one as it's Turn Based mode anyways.

3.3 Stealth Bonuses
There are two main Stealth Benefits: First, characters get a nice boost to their to hit chances.
Second, the enemies will be SURPRISED, which means they lose their first turn, unable to do anything, while your party gets a free and very powerful Alpha Strike!
Of course, both are highly helpful even on Tactician Mode.

High Ground is another important mechanic to master.
First, when attacking enemies below you from decent enough elevations, your characters will get a great boost to their to hit chances, just like in Stealth, another reason why DEX and Ranged Weapons are a great investment.
Second, enemies below you will have to hit penalties instead! A -2 that by itself will already remove the Tactician Mode Boost to their attack rolls.
Many areas in the game let you set up High Ground Ambushes, and you can even DESTROY the object you used to climb like a ladder so enemies cannot reach you at all!
Because of this it's important to first focus on the ranged enemies, as they're the ones that can still hit you from below.
However, because missile weapons require a Line of Sight which tends to stop at the edge of the surface you're at, remember you can do "Hit and Run" Tactics like moving to the edge, attacking the enemy, then moving back.
This way they can't target you at all!

BG3 has some differences when it comes to Spell Mechanics as opposed to D&D 3e or Pathfinder.

5.1 Concentration
Concentration is probably the most important new spell mechanic.
Most of the best spells in the game, including Buffs and Crowd Control, all require Concentration.
The main limitation is that you can only have ONE Concentration effect on the same character at the same time.
What this means is casting another Concentration spell will remove the first one you already had.
When you are hit in battle, even for 1 damage, you also have to succeed on a Concentration check not to lose the effect.

5.2 Preparing Spells
In BG3 you need to prepare spells before you can cast them, which can be done by going to your Spellbook and selecting what spells you want to cast from the ones you have available.
The good thing is unlike D&D 3rd Edition, you can freely swap between Prepared & Known Spells at will, you won't have to rest afterwards for it to take effect.

5.3 Recovering Spells
For most classes, a Long Rest is the only way to do so.
For Warlocks, a Short Rest will be enough, which is also the main way of healing your character's HP, and you have a limit of 2 Short Rests per Long Rest.

Lastly, remember some Spells can also be cast as Bonus Actions as explained before, and combined with another Spell in the same Turn!

Just like in the Divinity OS games, you can also create dangerous AoEs by combined elements.
The easiest way is to create a puddle of water first, from the Conjure Water Cleric & Conjurer Wizard subclass spell.
After that, any other elemental spell cast on top will change the surface to what you want, such as electrying or freezing it.
Best part is you can infinite cast Cantrips for some of that like Acid Splash & Ray of Frost.
The Level 1 Chromatic Orb spell also lets you create surfaces at will depending on the type you choose, but has a somewhat short AoE compared to Water/Grease Puddles (that you can set on Fire)

You can check enemies' sheet for stats and such by pressing T with the mouse over them.
This is extremely helpful because MANY enemies in the game have important and unique special battles that should and will change how you approach them in battle.
For example, an enemy that explodes upon death should of course be handled with ranged attacks, like Ettercaps.

While exploring the map, you'll usually get Perception checks to find dirt mounds.
If you have a Shovel, you can then dig for a nice treasure chest!

You can use the Dip ability as a Bonus Action to enhance the damage of weapons based on the elemental surface you chose.
For example, torches and other fire sources will increase ALL your weapon's damage, both melee and ranged, by +1d4 fire.
The duration is rather short lasting however, so it's best used during battle or if the source is close enough to the enemy.

Due to how open ended some areas in the game area, especially at the beginning, and how certain zones are definitely more difficult than others, it's nice to know where to go first, especially on Tactician Mode.
First, I recommend you go to the Emerald Grove, then head West for the Blighted Village, and West again for the Goblin Fort.
While there are MANY enemies there, most areas are easily cheesed through a combination of High Ground + Stealth as explained before.
After that you'll be swimming in nice loot and probably level 4, then you can go North for Gnolls, and also South for the Swamp.

Well, that was it for now, hope you enjoyed the guide and have lots of fun with BG3!