Go to Ammu-Nation and stock up on armour (don't mix and match armour, get shot if you need to use up weaker armour).

Go to a convenience store and fill up on snacks.

During the heist; you can use your interaction menu to resupply your health/armour (eat snacks while in cover to skip the eating animation).


Boost your strength to take less damage.
Start a Gerald mission, then go to the pier (or beach) and hit people, cops won't come (bodybuilders take more hits, more hits = more upgrade).


Go to a clothing store (Ponsonboys/Binco/Suburban).
Buy a heavy combat suit (only helps in heists) and a bulletproof helmet (helps in heists/freeroam).

Make a saved outfit of the suit and helmet (in store or at your closet).
You need to browse the outfits, it'll be under the "heavy combat suits" section (helmets are in hats).

Always use outfit during heists (select player saved outfits option).
You don't necessarily need it for the easier heists, but it definitely helps for bullets (it will slow you down, jumping lets you move faster).


Join a crew (one of the level up perks is increased max health).


I know there's a loading screen tip about it, but duck while in vehicles (including while being a gunner), you will take less damage.


After you finish the first heist, it'll unlock the Kuruma Armoured car for purchase (525k)
pretty much bulletproof, you can still get shot through the windows, but it'll take a lot to kill you (with more then enough time to resupply your armour/health).

Some people hate, some people like; whatever works...
explosions/rockets/remote bombs will blow the Kuruma up, and a heavy shotgun will remove the doors on it with a few shots.


I'm sure there's more, but that'll help get you started.