-This works better in online multi-player mode. After the first five or so waves, open the upstairs but not the door. Then, open the other stairs leading into the gun room. You will only need to worry about that room and the stairs. Have two people watch the stairs. The room has less obstructions to get caught up on and more space to move and evade. If overwhelmed, you can open the door but the next round will probably be your last.
-There are two ways to do this trick. Upstairs, over the first starting room, is a room with one window and a doorway with a window view. Use that door way to bottleneck zombies while someone else guards the stairwell and window. You can either unlock the door then the far stairs to keep your back free. Alternately, unlock the first stairs, leaving no protective sides. The only downside is that eventually you will need ammo. This works well online as long as you work together.
-Get to level three and leave a Crawler. Open the door with steps (not the ramp) and open the door that leads to the Thompson. Clear the debris and jump down to turn the power on. Then run out and make a right. Keep going straight to pass two windows on your right and a door on your left and right. Do not open the doors. From this area, kill the zombies that come down the path and have someone guard the window in the back. For the dogs, go to mainframe and hide by the fence in the corner by the window. When the dogs are cleared, go back to the path and repeat this. Do not forget to leave a Crawler or a zombie in the window. Also be careful with getting the nukes so you do not kill the last zombie and can get perks or whatever else.