Every survivor has a special ability that can be either used against the zombies or to buff your survivors. Make sure you know what each ability does exactly and then use them in the right situation.
Some abilities need a target, while others don't. Some abilities do great areal damage, others increase your damage output or even heal the building the survivor is in.
Especially in later nights, you need to take these abilities into account when putting your team together. The perfect combination will let you survive even longer!