Step 1: Choosing a Bike
Other things to look for:
If the bike has horizontal dropouts, it will work, but if you have the choice, get a frame without brazed on cable stays. They will only affect how your bike looks, but appearance does count sometimes, and single speeds look cool, so why mess with it.
Step 2: Break the chain
try to avoid pushing the pin all the way out, it's just bad form, but in this case it doesn't really matter since you'll be loosing several links anyway.
Step 3: Take off all the stuff you don't need
It helps if you remove the cable first, sounds obvious but don't forget.
any cable guide you can get off
All the cables also