Left 4 Dead Strategy

Left 4 Dead is a co-operative game, meaning teamwork will be of the utmost importance, vital at every moment in order for your team to achieve success. Nearly every gameplay system in the game is geared towards forcing you and your teammates to work together, including:

• Basic survival - Massive hordes of infected will be attacking you, far too many for one person to handle by themselves. Teamwork is required, not only in firepower but in formation - Survivors in front will need to duck down for their teammates in back in order for everybody to focus fire
• Countering boss infected - Many attacks from the boss infected involve entirely disabling one Survivor. When a Hunter pounces on top of a Survivor, that Survivor is helpless to stop it unless a teammate shoots and kills the Hunter. When a Smoker chokes a Survivor, the Survivor will die unless a teammate either shoots the tongue or kills the Smoker. When a Boomer pukes on a Survivor, that Survivor's vision is severely hindered and is about to get attacked by a couple dozen infected.
• Countering Tanks - The Tank is unique from the other player-controlled boss zombies due to its tremendous amount of health. This, combined with its speed and powerful melee and ranged attacks, means that it would be nearly impossible for a team to take out the Tank without every single Survivor focusing their fire. When you hear the telltale pounding of an oncoming Tank, make sure your entire team is aware and ready.
• Knocked down - In L4D, when a player's health goes down to zero, the player is knocked down into a "bleeding out" stage, unable to get up unless another Survivor helps them up. When helping another person up, the helper is unable to defend himself from any attacks, so it should be a coordinated team effort.
• Ledges - When a Survivor is about to fall over a ledge, they will automatically grab onto it, dangling helplessly until helped up by a teammate.
• Resource Sharing - Each Survivor may only carry one of each of the following at any moment: medkits, pills, and grenades. Survivors will need to share these precious resources. Will you be willing to give up your medkit when injured to somebody more needy?
• Knowing when not to shoot - The boss infected present a couple main situations when shooting is not the best thing to do. One good shot at a Boomer results in a massive explosion, hurting everybody in the area. Witches only become dangerous when disturbed. In both of these situations, teamwork and communication will be very important.
• Playing as boss infected - The three main playable boss zombies (Hunter, Boomer, Smoker) will really shine when working together. Combinations like the Smoker dragging a Survivor out of the pack right to a Boomer ready to puke or a Hunter ready to pounce, or a Boomer providing distraction while two Hunters sneak up and pounce from behind. As Left 4 Dead players get better at working together on the Survivor side, cooperation between the boss infected will become more and more vital to success.

With no game there's not a whole lot of strategy we can know or talk about. Do NOT freeze yourself to shorten the waiting process. Try coming back after release for more L4D strategy.

Sharpen your skills before release:
CS:S Zombie mod - Work on your zombie avoidance/killing skills by playing some Counter-Strike Source zombie maps (search for maps with the prefix zm_).

Zombie Panic! Source - HL2 mod, description from the official site:

The basic idea of the Zombie Panic is to create solid game play that is based on a classic zombie outbreak scenario, the living dead are coming for the last remaining humans, and these survivors must fight them off and live through the day.

The game works like this:

Everyone joins a server, in the beginning you can either choose to join the human team or you can volunteer to be the first zombie. If no one volunteers the game will pick one human randomly and the game begins. The starter zombie's goal is to, of course kill the humans while the human goal is to stay alive as long as possible, complete objectives, or even wipe out all the zombies. The catch is that when a human is slayed he will simply join the ranks of the undead, now ready to finish off his old living teammates.

The humans can't tell by the player list who's alive and who's not, eventually there will only be one survivor still standing if all goes wrong, facing all the zombies which use to be allies, with his back to a wall. The zombies only have a certain number of reinforcements (lives), when a zombie is killed they lose 1 life from the counter. However, when a human is killed they gain 1 life. If the zombies only have 1 respawn left the humans can win the round by killing off the remaining undead left on the map.

Other co-op games - There aren't too many of them, but games that do have some co-op include Gears of War and the Halo series on the Xbox and Xbox 360.