Here are some tactics for the house you find in the campaign.

Spawn. When you spawn you should go straight and find the gun on the wall. Buy it, if you are playing co-op both of you buy it. For a little bit get points to open the help room, then after a while go into the room and open the help box. Take the gun out of the box.

Try to unlock the upstairs if you are co-op, then make sure that one of your players has a machine gun and another has a shotgun. Shotgun, reason being its a heavy shot and if you move with it and have a machine gun covering your back you can get some serious kills. Machine gun, crowds of zombies can be taken with the shotgun so the machine guns is good to relieve the player while he's reloading (try not to hit your friend tho).

The tactic is to find a space where there is only one way to reach you. Have the heavy machine gunner standing over the shotgun and the shotgunner lying down. If the machine gunner is loading and shotgunner is loading, make sure you know that one of you should switch to the secondary (preferably shotgunner) because the shotgun is a fast reload.