Hi, these are just some common and uncommon tricks in Counter-Strike Source.

Running low on Ammo? Here's the answer: when you see alot of enemies and both your pistol and primary weapon's magazine is empty, simply drop the weapon and pick up your victim or dead teammate's weapon, it is faster than reloading, specially with the M249.

Enemies are camping? Ask a teammate to go with you in common camping areas, or if you have fast enough reaction time, go alone and jump to the corner, if you don't see anyone/anything quickly turn around before you land, this will be very easy if you change your mouse's sensetivity.

Carrying a flashbang and an enemy starts to appear? Throw the flashbang at their face! once you let go of the flashbang, immediately switch to your sidearm (if close range or point blank) or your primary (if they are a bit farther, use every primary weapon you have except for shotguns), fire at them or spray before the flashbang explodes, once you kill the target, run quickly.

Your enemies are pros? Distract them or get your teammate to do so, even if one of you guys got killed, he will be dead too, it may be risky but it will be worth it, specially if he is the last living player on his team. Or you can just do the FlashBang trick above.

Want to kill alot of players quickly, but you want to camp? Leave some bait, for example, leave an AWSM (AWP), AK-47, M4A1, C4 or any other useful items, hide at dark corridors (I suggest you use the Phoenix Connexxion skin to be less visible) and wait, If you can't buy an AWSM, just get the Team's objected Item (C4), or if you are a terrorist, let your enemy empty their magazines and they may return to their base to buy more ammo, this is where your teammates start to kick it, if you notice an enemy running, tell a teammate to go to their base just to be sure.

Want to cripple someone's ability? Knife them! Don't be afraid to knife them, even if you get killed, knifing them will make your victim paranoid, usually, they won't stop walking, this will make them easier prey for your bullets. Because knifing someone will be embarrassing for them and cripple their effectiveness in gun fights.

Is your enemy a Camper? If you know where they commonly camp, shoot through their walls, mostly, they hide behind crates, so shoot the crates.

That's all folks!

Hope this tips are helpful!