FRONDLY TIPS
#1: If you're surrounded by zombies, and you want your teammates to shoot them, crouch.
#2: If a nearby teammate is being licked by a Smoker, don't just follow the tongue and try to kill it. You can free your teammate by hitting him with a melee attack (these attacks do not deal any damage to teammates). Make a decision: if you can see the Smoker, and your friend isn't close by, shoot it; otherwise, consider whacking your friend instead.
#3: If you have to walk in front of people to get a shot at the zombies, let your team know so, and frigging crouch.
#4: Always watch every direction. Zombies can come from almost any direction at any time. If you hear the horde's song, a strategically placed molotov can be the difference between victory and defeat.
#5: Know what's going on. Discuss how you're going to use pain pills and med kits, figure out who should cover what direction, and stay close to your teammates in case they (or you) need a rescue.
#5.a: One decent system: Pick a partner, and decide which of you will lead, and which if you will follow. Wingmen need to watch their leader's backs and never seperate from them for more than a second.
#6: Check every room. You never know where the AI Director is putting stuff.
#7: Use quiet moments. Heal up, reload everything, check side rooms for supplies, and discuss plans for proceeding. Don't just rush toward the next fight.
#7.a: That said, don't linger in one spot too long. The AI Director doesn't wait around for you to be ready; it will continue to throw shit at you.
#8: Keep your weapons full. Always, always, always.
#8.a: Your shotgun will continue reloading, even if you're using your melee attack to push zombies away.