There is only one thing you ever need to think about in css and that is:
Is my gun aimed at head height? When you see people playing why are they walking around lookign down at peoples chests. Why make it so you have to moev your mouse up to their head? If you walk round a corner and there is someone there, all you gota do is click and booom head shot. Should be a constant reflex to put your mouse bakc up to head height.
If you walk round a corner and a guy is aimed at your chest and your gun is at head height. Unless he gets a very lucky spray or your reflexs are appaling he should be dead.
Also if you are a italy player and yu wana get top score in the game. An easy way is to go T and go into t side apartments, aim at the door from a off agle (not 90degrees to the door) and there head will appear just as they walk about mmm half way down the lil L junction corridor into your side and you can pop it every time. Racked up so many easy kills just doign that alone. Its amazing how many people beleive that if they walk slower at you they can pop round and kill you. No it just makes it even easyer for you to hit them!
And once perfected you stand pritty close to your exit door. it means they can never flasjh you properly as you can run out and back and still be ready to kill them when they run into your side.