Counter-Strike: Source/Strategies

Footsteps
All players run when moving by default in Counter-Strike: Source, and if you're quiet, you can hear their footsteps. This can help pinpoint where people are if they're close to you, or when to shoot if you feel somebody's about to pop out from around a corner. Players who walk instead of running (by holding down Shift by default) make an almost inaudible amount of noise, and so this tactic doesn't work. Crouching will also soften the noise you make.

Flashbangs
Flashbang grenades will blind anyone who sees them go off, or a reflection of them going off; and deafen anyone within a certain radius (to a lesser or higher degree depending on their distance from the grenade). Although they will not hurt anybody, if somebody is caught in a flashbang "explosion", they will be incapable of a co-ordinated response to any attack, and will be an easy kill. Flashbangs should be preferably used against groups of enemies, and you should only attack if you're sure the flashbang has been effective. Flashbangs may be bounced off walls when thrown, but you must always remember that the "hitbox" of any grenade is slightly larger than you might expect, so if throwing one close to a wall (perhaps over a parapet), you must remember to throw it slightly further away from the wall than you might normally do so, to prevent it bouncing back.

If caught in a flashbang "explosion", the best thing to do if you remember your surroundings sufficiently well is to move for cover. If you do not remember your surroundings, you should at least crouch down. If you're completely blinded, it would be useful to reload so you can be prepared for any pending onslaught.