Well the most important thing i was ever told, by one of the top CS players was: 'Play Smart'. Choose the right weapons for the job, try to think what other players might do and what they just did. This way you sort of get to know where players will be. It's a little hard to explain, but i'll try:
A CT sniper just took out 4 people down the pass on dust, if he's not too cleaver he's gonna be in the same place next time. So if you can't afford a rifle don't go down there.
You see what i mean.
It's sounds a little far feched, but you really have to think about what the other players are likely to do, by what they did last round. You see what i mean.
I apologise if you just wanted to know simple things like fire though boxes etc. Don't laugh at me but 'Play Smart' was the most important thing I was ever told.
jump only when you have to because of the slowdown
if you are trying to look around corners, dont slowly peak cuz chances are your enemy has the same idea. if you want to check run and make it quick.
many people say the glock is "useless" or a "pea shooter." truth is its an effective gun if used right. when you shoot an enemy is slows their movement big time, personally i prefer semi-auto instead of burst fire. if your in close combat with it, try running around the enemy in a circle, s/he may have trouble trying to pinpoint you.
You know until today i would have said the glock was rubbish, but i've never really used it, but i just got a wicked (well it might not be in other peoples cases) score, and i got loads of glock kills.
I love the glock now.
I did get 60 - 2 once, can't find the picture now, i'm so damn inconsistant.