This will show you and your fellow co-op partners to survive.

What you have to do is to stay in the start building for as many rounds as it takes you to get about 2000 points. Then open the help door and get a gun from the random box. If you have got the M1A1 carbine and you got it before you bought the random gun from the box, then swap the M1A1 carbine for your pistol and swap the random gun for your pistol. The M1A1 carbine can be used as a reserve gun.

Clear the debris from the stairs (in the help room and when you have enough points) when you go up go to the grenade outline on the wall, this is the best place to make camp. Stay there and keep the camp there.

Always stay together! Never go off alone. If one person is downed then let the other people protect while the one other revives. Always look out for each other. If one person absolutely has to go to get another gun or to get something else then go together never alone. You need to work together to survive!

If you are wondering then why you should stay by the grenade outline, it is so that you can always have a supply of grenades to kill several zombies quickly, and it is one of the places where there are only 1 entrance around it.

Hint 1: don't clear the other debris leading down to the starting room unless utterly necessary for your survival.

Hint 2: Don't ever waste points, it makes it easier to survive and also then you have points to spend on essential things.