The first thing to do is run to 20-25 and hit enter to turn on the power.
Then kill 5 out of 6 zombies on round 1.
After you have killed 5 zombies, open the first door.
Then run all the way right and kill the last zombie.
Stay at this position until you have enough points to open the second door.
Now if you are low on health you can run right for a while then run back left and your health should get to full.
Go to 81-0 and kill zombies, make sure you walk right slowly so a zombie does not get on your right. Do this until you get to round 4.
On round 4 kill most of the zombies, then run to the box and get your first gun.
Now get your second gun as soon as possible.
Ratings for the guns and how to use them are here.
This is the worst gun in the game.
Not much better then the M1911, try to get another gun as soon as possible to replace it.
One of the best guns, try to only use it when instakill is active.
The best gun in the whole game! Never replace it.
Thanks for reading.