Left 4 Dead 2 Cheats

First off, I can't guarantee that these cheats will save each of your teammates. The apocalypse is dog eat dog, so the following tips are to insure your own survival.
But these are secretly obvious ways to combat the attacks of each type of special infected.

Hunter: Zig-Zag Maneuver! Once the Hunter leaps, it cannot change direction(mid-air). If you find yourself spread out from your teammates and spot a hunter coming after you, start moving in random, jagged directions! It takes some getting used to, but you can run back to your team(and have them kill the Hunter) or multitask--zigzag away and shoot the Hunter simultaneously! Kickass!

Smoker: They are not known for being fast runners. Specifically, if you find yourself snared by his tounge, and a nearby teammate saves you--but leaves the Smoker alive(by melee shoving you or shooting the tongue)--RUN AFTER THE BASTARD! The Smoker is paralyzed for a few seconds after his tongue is broken, giving you a headstart after him.
To prevent being snared in the first place, run directly in front of a Smoker. Since he depends on his tongue to drag you long distances, if you're close to him, he is useless and attempts to run. Shoot his retreating behind!

Boomer: What's the worst it's gonna do? If you're bound on killing fatties, just run up and kill it. Melee Weapons and Shotguns (hell, even Magnums) only take one shot to kill the Boomer. They are, however, very prone to stumbling, so run up and shove it away, back up fast, and shoot. How can you miss?

Spitter: The Spitter stands taller than other infected and run in a peculiarly different way. This makes them easier to spot.
ALSO, a neon green trail of spit come from their mouth while they run. It means they stand out.
The easiest way to kill these revolting creatures is to run up to it as soon as it come on screen, and as you (nonstoppingly) run by it, use a melee weapon kill it. So long as you keep running, the acid that forms upon a Spitter death will not have spawned yet, and consequently, not harm you.

Charger: I love Chargers. Like Hunters, once they decide on a direction to charge, they cannot stop or turn. So man up, take the bull by the horns, and stand in the Charger's path (perferably a few feet away, giving you time to move). As soon as you hear the Charger's signature ARAAWWWWWWWWWWWWWWWWGH yell of "I'm Running!", take a few steps to the left or right. He'll just keep running further away from you.
ALSO, another way to... 

A really easy way, i've found, to get the achievement "Tank Burger"(kill a tank using only melee weapons) is to go to Single player campaign and select No Mercy on Easy. Select the chapter Sewers and pick any character. Find a melee weapon and lead your team to the gas station. If you shoot the gas station with the other bots by it, it'll blow it up, and incapacitate or kill your team. Then try to get through the level and find a tank. If none show up, go back to the main menu and try again. Then, try to kill the tank with melee weapons. try to move in circles and back and forth so it may swing it's fist and miss. that's the perfect chance to swing your melee weapon. This may take a couple tries, but if it gets shot at all, you can't get the achievement. Another way may work with friends all picking up a melee weapon and surrounding it. a good place would probably be on Dead Center chapter 1, because then everyone could start with a melee weapon.