The 10 commandments of Left 4 Dead

Thou shalt not think thy is invincible when thy hast thou automatic shotgun, as thou knowest not when thy Tank shalt spoil thy plans of World Zombie Domination.
Thou shalt have one player to watch thy rear, for thy Smoker is cunning and sneaky.
Thou shalt not split up unless thou wantest to be ambushed by thy Hunter.
Thou shalt shove thy Boomer away before shooting him.
Thou shalt not rush thy enemy if thy hast a player with thy sniper rifle who hast clear lines of sight.
Thou shalt not disturb thy Witch if thou health is low.
Thou shalt not hoard thy health pack if thy teammate is near death, for four players killest thy Horde better than three.
Thou must learnest that thy sniper rifle does not helpest thy team during thy final battle.
Thou shalt not abandon thy teammates and quit thy game before thou hast escaped.
Thou shalt not fight over who playest as Zoey.