In the starting room, go through the door on your right when you have enough points. Then open upstairs if you have a spare 1,000 points.

There should be a wall in the middle of the room upstairs with a pillar sticking out of it.

Sprint towards the pillar where it joins the wall, then jump and go prone when you hit it.

Turn around so you are facing the stairs. Now half of your body should be in the wall.

In this position, you should have a clear shot of all upcoming zombies without them attacking you. It is advisable, however, you also have a deployable machine gun and a ray gun.

Also, make sure that the other player covers the window behind you, otherwise the zombies can attack you from behind.