Retail value vs. Trade-in – Know right away: you are going to take a beating. You should only trade in if you just don’t want the headache.
Sell it yourself – Appearance is a big part of selling your car yourself. Have it detailed (usually less than $100), and make sure your car has good (and good-looking!) tires on.
Maintenance – Keep good records of oil changes, repairs, maintenance, etc. Make sure there aren’t any weird noises or vibrations. If helps if your fluids are topped off and clean, and make sure your car drives STRAIT!
When you’re preparing to sell it, know the value of your car using a NADA book and newspapers (The value is determined by miles, equipment and condition.). If you run a classified ad, price the car a few hundred dollars more than you want, so that you can negotiate with potential buyers.