Don't be lured by a salesperson who offers a sweet-sounding deal that "expires today." Instead, research the car's dealer cost and the Edmunds.com True Market Value (TMV), which can serve as a benchmark for your negotiations. Also get preapproved for a loan, and then see if the dealer can beat your finance rate.
A dealer claims you can't get a DVD system without buying the sunroof too? Don't take his word for it. Visit the manufacturer's Web site to see whether your preferred features come a la carte or bundled with other options. If he doesn't have the exact model you're looking for, ask him to order it—or shop around.
Reduce sales pressure by asking the dealer's Internet sales manager for a quote by e-mail or fax. Make sure the price applies to an in-stock model (ask for a vehicle identification number), and take along a printout when you show up to buy it.
You'll probably get more for your old car by selling it yourself. But if you prefer to let the dealer handle both transactions, check your trade-in's TMV on Edmunds.com, and negotiate the price separately.
Read the final invoice closely. There's no way to avoid the destination charge or registration costs, but you should question any suspicious add-ons, such as dealer prep fees.