Left 4 Dead

Be careful not to shoot your allies. It is not worth killing two zombies if you have to down an ally to do it. Do not bother searching for items. The longer you linger, the more zombies will spawn. However, if you see something along the way, feel free to pick it up. However it is probably not a good idea to go out of your way for it. If someone gets pinned or grabbed by a Smoker, sometimes it is easier to free them by simply going up to them and pressing the LT  . Most people think you need to run from the Tank, but even under the Easy and Normal difficulties you must to kill two Tanks before the rescue vehicle arrives. Therefore it is not possible to run all the way back to the safe room. The very best way to kill the Tank is to have everyone fire at it while the person it is after tries to dodge and fire at the same time. Even under the Expert difficulty setting it should not live more than a minute if everyone just stays calm and shoots at it. There is no way to pass the Tank without shooting it. Although if you are at the start it might be a good idea to go back, but during the infinite horde during the finale it is not logical.

When using melee (LT), press Y, LT repeatedly. You will switch weapons and melee. This helps to complete the game on the Expert difficulty from hordes of attacking zombies.

Rapidly tap [Melee] and [Weapon Switch] alternately to double your melee speed.

Select Survival mode and have the M16 equipped with a full clip. hold LT to start melee. Quickly tap Y(2). Hold RT for approximately 5 seconds. Release LT and you should fire all fifty rounds in one burst. This is useful for tanks.

Tanks will float when dead.

Note: This has only been tested on No Mercy. Enable the "Play against NPCs only on Versus Live" glitch. Kill all of the survivors. Then, go back to the respawn point. Have all of the infected up on the rooftop. Jump down on the Hummer. It will kill all of the infected. Wait for a few seconds, and you will now have a free roam camera, like on the PC version of the game. There are no secrets, but there is a mini-city of No Mercy underground that is very interesting.

Use the following trick to get a free roam camera without all NPC characters. Note: This only lasts for a very short time. It also works best if you are at a place where people can jump off somewhere to die. Have a rigged team, where four of your friends are on the NPC team and three of your friends are on Infected. Then have all eight people jump off. They will all die, and you (The Infected) should have a free roam camera. Note: This was tested on No Mercy: The Hospital.

Okay in the first level if you don't won't to go through all of the house you can skip it.

After you pick your weapons you can see a place in the roof were you can jump through the glass. Go to the edge and jump on it, across on anoter building (look down a bit) you should see air conditioning boxes. Jump down on them and then then jump on the dumpster and you are there.

A Tank and Hunter can revive you if you become incapacitated. Hold X when you are near an incapacitated person if you are infected.

In some of the newspapers seen throughout the game, Dr. Breen from Half Life can be seen.

When Louis is picking up a sub machinegun, he might say "Aowww man this is just like Counter-Strike!".  This audio file can be played directly through the "TakeSubMachineGun03.wav" file in the "\Program Files (x86)\Steam\steamapps\common\left 4 dead\left4dead\sound\player\survivor\voice\Manager" directory.