Master the art of straffing (obviously that means moving left to right) and then finally straffing and shooting . the objective of this is , while moving left to right is that the moment you start to go either left or right while you are in the very middle of the straff your bullet is about 100% accurate so if you can learn to shoot while you straff you will be one step ahead in terms of shooting / aiming .
also I suggest binding jump to your mouse wheel down and learning to straf and jump other wise known as bunnyhopping.
Use your radar it will tell you more then your team mates are going to tell you , most of the time .
a good set of headphones can save your life that being said .(Walking will save your life , where running will more likely get you found and killed)
google css bind if you have a mouse with buttons on the side I have found it very uselful to have my HE and Flash grenades bound to my mouse then once you have your prim wep out all u ahve to do is scoll up to get your smoke out .
Don't give up this game has a certain way with people and making you rage .
forget about buying helmets they do nothing
I suggest the helmet I have heard many a "DING" and knew that helmet saved me :P