Smoke and Flash

Use smoke grenades to provide cover when none is available

Smoke grenades can help provide cover when you're under sniper fire and won't survive a charge. Note that smoke billows out of the grenade slowly, in a rotating pattern -- so make sure you're on the right side of the smoke if you want to take advantage of its cover. Note that the obscurity goes both ways -- if they can't see you, then you can't see them. Excessive use of smoke grenades is often considered exploitative, since it is sometimes used to malicious reduce frame rates for others. Use smoke for cover -- but quickly, before the smoke fades away and leaves you exposed.

Use flashbang grenades before charging

Flashbangs are one of the secret weapons of Counter-Strike. Flashbangs blind their opponent, for a period of time that depends on their proximity to the blast. A flashbang at close range, for instance, can leave the victim completely incapacitated for a full ten seconds -- an eternity in close quarters combat. When you know the enemy is lurking around a corner, a flashbang can be a devastating softening up weapon: Throw the flashbang, blind your enemy, and then charge and finish him off. Note that due to their relatively short duration, flashbangs are not very useful unless they are followed up with an immediate charge. Needless to say, take care not to flashbang yourself or your own team.