I recently started a thread that talks about what is the best inexpensive bike to get to sell. Well you aren't going to sell yours but a lot of the info would help you. I will attach a link to it for you but I just want to give you a summary.
Make sure it has front and rear brakes. Also if it has cheap fenders and fender mounts either replace them or beef them up. Last thing is watch for cheap wheels. Thin spokes and cheap hub bearings in particular. I came to the conclusion it is best to find a good bike that is used.