1) Shoot In Burst Fire
Counter-Strike tries copy the reality so the longer you hold down the trigger the less accurate your rounds become. So after you shot few times you will likely just be blasting ammunition into heaven, far away from your enemies. For accurate hits you should fire in short bursts of only two or three rounds, giving you a chance steady up for the next shot.
2) Watch Reloads
Reloading is important. While you're reloading, you can't use your weapon so you should watch your ammo and plan the best time for reloading your gun!
3) Your Pistol Is A Gun Too
In Counter-Strike when you're out of ammo, it's faster to switch your weapon to pistol and shoot down your enemy with it then to wait for reloading your primary gun. Sometimes a good Counter-Strike player will finish the enemy off with his pistol or even his knife rather than wait for a reload.
4) Customize Keys
You can configure some scripts under your favorite keys to make some acts faster then normal. Fast weapon changes and other things. You can find thousands of config files ready to use, it's just about your preferences.
5) Jumping Is Important
When you appear in an open area or you know about snipers waiting for you, it's important to move around unpredictably. Jumping (not too regularly), can force your enemy to miss you or to shoot you in a part of body with less damaging then your head.
6) Use Grenades
Grenades are another chapter in Counter-Strike. You can have only limited amount of grenades to it's imporant to use it carefully. A common approach is to soften the enemy up with a few grenades before going in for the final assault. Flashbang grenades, has function to temporarily blind those caught in the blast radius. Of course, a grenade can also come in handy if you need to buy some time to make a quick retreat, or create a distraction.
Advice: Aim before you shoot! Why not take it a step higher, don’t just aim, AIM for head-shots. As you’re playing Counter Strike, make it a game to never miss a head-shot. That means you come to a near dead stop, aim for your enemies head, and click with near 100% certainty that you will not miss. If you’re using an automatic weapon, 1 short burst is all you should need to get the job done.