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.