I would add some things to this tips list, like:
1. Look for boxes. At leas some guns, bags, vests, ammo pouches and similar junk for usage/vendoring is always there. Although why this is the case - beats me
2. Use grenades. Preferably from your pockets. You can activate (via right click pop out menu) them and throw them WITHOUT switching weapons (just drag them as if you would like to throw them on the ground, just remember to HOLD that mouse button
). This is perfect, if you need to just make a quick run away from a squad of baddies, who are facing you. Lob a grenade and while they are shocked - run to a safe spot. Also - insta-activating-and-throwing work both ways, so do not expect mercy from AI if you stick in a bunch.
3. Use house corners with double level firepower, i.e. prepare an ambush at the corner, with two mercs waiting around it: first - crouched and aimed at the corner. Another standing right behind him aiming at the same spot. Something like musketters
4. Use alt+cursor to make a quick turn around the corners. Take a shot or two from hip, then get back to cover in the same manner via alt+cursor.
5. When you run sideways - you are a hard target. Use that do distract AI AND lure them to a nicely prepared fire zone
6. Save often =)