We have a lot of newer players that haven't played 5e or EA before so I though I would put together a quickie guide for your ability scores and how to plan them out.
Rule 1 : Always aim for even numbers when you are first starting out. It is more cost effective because odd numbers give you the same bonus as the even number below it. e.g. a 17 in Dex gives you the same +3 that a 16 does.
Rule 2 : Put a 16 in your class's main ability score. All classes have a primary ability score that affects their capabilities. The game puts a star next to that stat so it is easy to figure out. Do note though, that Paladins and to a lesser degree, Rangers, have 2 abilities they have to take into account. Their primary attack ability and their spell casting ability. You have to balance those out based on your goals with that character, but in general a 16 in their physical attribute and a 14 in their spell casting is a good place to start.
Rule 3 : When in doubt put your extra points in Con and Wis. Both of those stats protect you from dangerous spells and the bonus HP from Con is a great perk. If you have a single point left and your Str is less than 13, put that extra point in Str, it has the only significant boost for an odd number, which is carrying weight.
Rule 4 : Be careful with dump stats. A 'dump stat' is an ability score that you give an 8 so that you can use those points towards something more important. Often you'll see melee characters with an 8 in Int and Cha so they can pump their physical stats through the roof. However in BG3 there are a lot of skill checks of all kinds, and having a negative score can lead to a lot of conversation failures. On the other side of the house, casters who dump strength are in for a bad time when the enemy tries to push them off a cliff and being over-encumbered gives you disadvantage on multiple checks that you don't want to mess up.
Rule 5: This is more of a shorthand for planning your spreads than a rule, but the quick math for your scores can be summed up in pairs of numbers: 8/15, 10/14, 12/13. What that means is that for every 15 ability score, you get an 8 ability score, etc. You can obviously shift points around from there, but for a quick double-check those pairs come in real handy.
Rule 6 : Use your free +2 on a 14 and your free +1 on a 15 or 13. The way ability score point buy works is that every one score increase from 8-13 costs one point (out of 27 total), while going to 14 and then 15 costs two points each. Your free +2 and +1 ignore that rule though, so you basically get even more free points if you spend them to get to 14 or higher.
Rule 8: Plan for the type of armor you'll be using. Your Dex bonus gets applied to your AC differently based on your type of armor; for light armor you get to add your entire bonus to your AC, for medium armor you get to add a maximum of +2, and for heavy armor you don't get any bonus from your Dex. By knowing what your wearing (combined with rule 2) you can better plan how to spend your points on Dex.
Rule 9: another not rule, below are just some good combos for different classes based on the assumptions that you'll be using them in one or two standard ways. I'll be doing at least two spreads, one with dump stats and one without. Your MC is going to have to make most of the ability checks on their own, and you don't want to shoot yourself in the foot before you get a handle on the basics and/or are willing to accept failure. so use the dump stat version at your own peril.
The stat order is Strength Dexterity Constitution Intelligence Wisdom Charisma. I'm not typing those out each time. The numbers will have the base scores followed with a 1 or 2 to indicate where to put your bonus points.
Barbarian, Strength based medium armor fighter:
14(2) 13(1) 14 10 12 10
14(2) 14 15(1) 8 10 10
Heavy armor tanky fighter
15(2)* 12 15(1) 8 12 9 Pick up Heavy Armor Master for the +1 Str and the extra defenses to basic damage. This feat is better the lower your level, so get it first.
Caster Bard, Warlock, Sorcerer:
10 13(1) 14 10 12 14 (2)
8 14 15(1) 10 10 14(2)
Cleric, Druid Caster:
12 14 13(1) 10 14(2) 10
10 14 15(1) 10 14(2) 8
Moon Druid:
11 12 13(1) 12 14(2) 12 you don't need to waste a lot of points on your physical stats for combat purposes, since your wildshape will overwrite them.
Monk:
10 14 13(1) 10 14(2) 12
10 15(1) 14 8 14(2) 10
Heavy armor Paladin:
14(2) 10 14 10 12 13(1)
15(1) 10 14 8 10 14(2)
15(1) 8 15* 8 10 14(2) take Resilient Con as your first ASI to take it to 16, this will make you the tankiest you can be with your aura backing you up
Ranger:
12 14(2) 14 10 13(1) 10
10 14(2) 15(1) 10 14 8 - melee
10 14(2) 14 10 15(1) 8 - ranged
Rogue and Dex Fighter:
11 14(2) 15(1) 10 12 10
Wizard:
10 14 13(1) 14(2) 12 10
8 15(1) 14 14(2) 12 8
Special cases:
Dex Caster Fighter
10 15* 14(2) 15(1) 8 8 take Resilient Dex as your first ASI to take it to 16.
Caster Rogue
10 14(2) 15* 15(1) 8 8 take Resilient Con as your first ASI to take it to 16, this will help with your concentration saves.
Melee Bard
8 15(1) 15* 8 10 14(2) take Resilient Con as your first ASI to take it to 16, this will help with your concentration saves.
Warlock Pact of the Blade and multi-classes that utilize it (Paladins and Melee Bards):
10 14 15(1) 8 10 14(2) here you can maximize your defenses since both your attacks and your spells are working off of Cha.
Your mileage may vary and you can always switch around the 8,10, and 12s. The 14s and 16s are more important to leave where they are, though there are some places where it is dealers choice on 16 Dex 14 Con or vice versa.
Anyway, if the hour I spent putting this together saves some of you time, then I am glad to have helped