Skip First Boss Battle
When you encounter the first Thing Boss, hold Up/Left and you should run under it before it can hit you. This will also aim you directly at the junction box. Immediately start fixing it. As soon as it is almost fixed, hold Right to run through the door. Since he will still keep fixing it as long as you release the button, with luck it will be fixed before the Boss attacks for the third time. At the intermission sequence you tend to take off in a random direction, so this may take a few attempts -- save immediately before trying this. If successfully completed, you will only lose only about half a bar of health and no ammunition, making the next area much easier.

Skip Second Thing Boss
When standing in the warehouse just outside from where the second Thing boss lurks, you will notice a garage door to the left of the Boss's door. Get an ally to stand near the garage door, then back up and throw a grenade at them. If done properly, you can cause the character to run towards the door and it will open. Run inside before it shuts and watch the video.

Unlimited Flares
Highlight ''Flare'' and enable it but don't throw it. When it is low, press Left or Right and highlight another object. Then, highlight ''Flare'' again. It will have restarted and you will not lose another one.

Hidden Trailer
At the main Menu wait at least one minute or more for a uncut tv trailer of the game

People Persuader
If a person's trust is in the orange and they won't cooperate go to 1st person mode and aim the gun at their head for 3 seconds. Now they will!

Shutting Doors
Always shut the door of the room you walk into, if you have the chance. For example, on the level where you have to kill all the walkers, a walker will enter from the front door if you do not shut it.

Infinite Ammo
At Main menu, go to options and hold L1, R1, L2, R2, then press square, circle, select, left, right, up,up,up,up, square, right, x, x, x, x, x, triangle