Playing Guides

[Bastet]

When the zombies made a whole in a door, shoot through it.
 
Another guide here on L4D @ Bit-Tech

From this:
 
There’s an addendum to this though because at the moment, fire damage is cumulative - that means if you throw three molotovs they cause three times the damage per second. Seeing a hunter trying to light himself in the fires of four molotovs and a gas canister can warm you with schadenfreude.
 
Is this still true?
 
About gas bottles/cans:
 
They are fun to use and will do significant damage to tanks if you can get your timing right. If you do manage to hit a tank with one it will stumble away from the explosion, which means they can be used to shove tanks off the roof, as in the end of No Mercy’s fourth map.
 
Edit: on tanks and fire:
Tanks are the most difficult infected to kill. The best way to go about killing them is to set it on fire. As soon as it’s set alight an invisible timer starts, and when the timer reaches zero the tank will die, no matter how much health it has left. On normal a tank takes 30 seconds to burn, 35 on advanced, and 40 on expert. The tank can run faster when on fire, so be extremely careful!
 
Witch:
The best way to pass the witch isn’t walking slowly with your flashlights off. Flashlights have no effect on the witch – whether she wakes up is a calculation based on distance and the number of survivors in her vicinity. Give her a wide berth and nothing will happen to you. If you’re in an enclosed space with the witch one player should pass it at a time. Run past the witch at full speed – or if you’re feeling particularly confident, some players have even been known to jump over her. The next player should wait until the witch has calmed down again before they pass. All four survivors can pass her in this manner.
 
Score:
The health bonus works off both the medpacks you’re carrying when you get into the safe-room, and the health of your team. Many people think you have to use your medpacks to increase the bonus, but this isn’t really so as they’re factored into the score. It’s more important that you get the safe-room door closed as quickly as possible to conserve your remaining health.

[RizZy]

I just stumbled across this, it's an interesting little read if your into taking out witches - http://boomercharged.net/2009/01/25/803/

[Dr Sadako]

4. Dealing with;
    Witches - Avoid. Turn off your flashlights, go slowly and creep past if you can. Now.....assuming you are playing versus, that's going to be hard as there will be smokers, boomers and hunters all hanging about with her, stroking her hair, acting like ugly sirens trying to draw you in. If you have just passed one wave of 'bosses' then some concentrated fire will help. As will a face full of molotovs.

Thought this was in order to bump. If you hear a witch start by turning off your flashlight and when you are closer walk instead of run. That way you will decrease the chance you will startle the witch.

If you need to kill the witch use a shotgun and shoot her in the body (from behind or the side) at close range. Have a look at this video and you see how it is done. Also check the link in the post above.

[Benny]

If I remember correctly it's more to do with the quantity of survivors in the area.

You can just sprint past them as long as you do it one at a time with a reasonable gap. Get pounced or swarmed whilst doing it and you're in trouble.

The best way, other than a shotgun to the face is for whoever has the lowest health to take the hit and then heal once she's dead. Never heal before you go after her.

[Benny]

L4D2 Info here...
http://gamingbolt.com/2009/11/20/a-guide-to-the-special-infected-l4d2/