1. Locate an old road bike or ‘city bike’ (I’m sure you know this, but I would make sure the
rims are true.) In looking for your bike, try to find one with horizontal dropouts, see:
http://www.singlespeed.net/tension.htm
You can still make a fixed gear with (the more common) vertical dropouts but you
will have to readjust and tighten the back hub a lot.
2. Remove all the shifters, cables and cogs except the cog you choose for your preferred ratio.
3. You MUST get a thicker chain than a normal road bike chain, as you don’t want a chain snapping on you. BMX chains work and they are cheaper than track bike chains.
4. If you are not used to fixed gear, I would leave the front brake on. Some people like to put a BMX brake on the front.