Kill the following special infected by using the corresponding strategies:
Boomer Shoot it in the stomach while keeping your distance.
Charger Get close to it to prevent it from charging, and then it will only be able to inflict one melee damage.
Hunter When it is in its pouncing position, use a shotgun to push it back, then shoot it in the head.
Jockey Get into a huddle with your teammates to prevent it from launching at you, and wait for it to appear. Have all teammates shoot the Jockey at the same time.
Smoker Get close to it to prevent it from using its tongue to grab survivors from far distances.
Spitter Shoot at the head, and dodge when it spits.
Tank Go to higher ground, and shoot at it while dodging it. In Co-op mode, use a grenade launcher for a frontal assault while your teammates fire at its back with shotguns. Alternately, do not try to deal any damage to the Tank, but instead hide somewhere and let the survivor A.I. kill it.