Here is how I always get to a high level on Zombies (Kino Der Toten, solo),

-Level 1: just stab, no shooting.
-Level 2: you are allowed to shoot some times.
-Level 3: Get the M14 or the shotgun, I say the M14.
-Level 4: Start throwing atleast 1/2 grenades.
-Level 5: (If the hellhounds come, open the bottom door) Kill some zombies, then open the top door.
-Level 6: Get the AK74 if you went through the bottom, or if you went through the top, get the Stakeout.
-Level 7: (Dogs might come on this level, or came previously on level 6 or 5) Go where you turn on the power, but don't turn it on.
P.S. When the hellhounds come out, get to a corner and kill them all.
-Level 8: If the Randombox is in that room(or the dressing room), get one gun, don't waste all your money!
-Level 9: Try to kill all the zombies, leave on up, go on the teleporter, hold Square(Xbox: X, I think), and go to where you start in the beggining of the game, then kill the last zombie.
-Level 10: Doggies will probably come out, so stay on the teleporter. When alot of dogs come out, use the teleporter. I used the "Pack-a-punch" thingy(where you upgrade your gun.) Upgrade it, then throw grenades where the zombies are at. (Buy more grenades, optional.) Might go to a random room, I think they just try to scare you. When you go back down, you will be in where you start in the beggining.

Then try to go arong there, killing, also go to the Randomboxes a few times.
note about the points: When your going to teleport, have 5000 points(if your going to upgrade your gun), or throw grenades from up there. The highest level I've gone up to on my own is 40!
P.S. I gotta new username, for mii own! :3 (PS3)