You're going to need pictures, know the model and be able to answer the answers to the questions on this website:
Price vs Condition
Any savvy buyer will have visited that site as well.
As far as ID'ing the model, you may be able to narrow it down here:
Do you have the title that can ID it? Or the VIN #? It can be deciphered by someone here if you do. Once you've done some homework, you can list it on the Classifieds (see tab @ the top of this site).
Good luck with your sale!