Do's and Dont's- basically just follow the list and you will be alright, common sense applies...
Do's-
Stock up on ammo
Always have a few pain killers and morphine shots.
Move quickly and as quietly as you can thru town, avoiding zombies is a must for staying alive. One shot will let a bandit know where you are or that you are in the area.
Call out your target if your playing with a teamate, shooting randomly or at a bandit without communication can cost lifes.
Carry a few uncooked meat for those tricky situations, once you cook the meat it will heal back 800 blood and you can do it on your own unlike blood bags
Use the Q and E keys to lean around buildings to get better shots without exposing your whole body, imagine it like a more amazing quick peak.
Dont's
Stay along the coast move into the hills after getting the supplies you need.
Shoot at targets if you are not sure you can kill them quickly
Shoot your weapon in hte middle of a town, unless you are inside a building.
Stay in one spot too long
Sprint in towns
If you have any more questions about the game or you want to play (all you need is ArmA2: Combined Operations) we can help you get set up and all that.