Who still plays CS 1.6 here? It's the only online game I play nowadays, mainly because it requires zero preparation (unlike, for instance, MMORPGs)

Well I'd like to know some tips, whatever your experience has told you, and I'll share some of mine too.

For instance, it's a bad habit to duck whenever you see an enemy. Ducking improves your aim at the cost of being still. When ducking, a chest shot might end up as a head shot, so it's easier for others to HS you. It's much better if you simply strife left-right. Try not to strafe too much from one side, and try not to strafe too quickly because you won't move much from your starting point (and therefore easier for others to kill you).

Another tip would be to listen carefully to the footsteps, because they often reveal the enemies' location.

Lastly, don't reload often. If you've got an AK-47 or M4, 10+ bullets are sufficient to kill someone (from short distance). Don't reload once you've killed an enemy, try to reload when you're certain that most (if not all) paths that end up in the room/pathway you're in do not have enemies.

I still play 1.5 though, with bots. You should try Serious Sam: the second encounter, you don't need any preparation either, but it's fun. A very sharp marksmanship is not very necessary, but a good sense is still required.

One thing to add, the best part is it's online cooperate mode.