What's the Best Strategy for the Nazi Zombies?

Yo guys! I want to know what's your best strategies to get far in the Nazi zombies level. I played with Dez and the both of us could only get to level 16 on our own. Got any advice?

Also this place needs more chicks here

i havent played by myself do less zombies come if your by yourself?

Dude, I said I played with my cousin Dez. Not by myself. I want to know some tips for two people. Since apprently I suck to her and need some advice

All you have to do is both of you get a ray gun, shotgun, or any other fast gun.
Go upstairs through the help door.(its important you dont go through the main room) After you go upstairs go through the doorway with the window and sit in the corner under the grenades. With 2 or more people this should be easy since all you have to worry about is 1 window and i doorway. Doing this I got to level 22 with a friend.