Don't give in to pressure tactics.
Signing a buyer's order or placing a deposit should NOT be done during negotiations, but only AFTER you have comparison-shopped and made your purchase decision. A dealer who really wants to sell you the vehicle should be willing to hold the offer open for a day or two while you compare and decide.
Separate the deal into key parts.
Keep the main components distinct so that you can consider and maintain your options. Negotiate (1) the purchase price, (2) the trade-in value of your old vehicle, and (3) the financing or monthly payments, separately and in that order. In this way you can choose whether to trade your old vehicle or sell it yourself, and whether or not to finance through the dealer. When these items are not discussed separately, confusion can result, as changing one item may also change others. For instance, the monthly payment amount may go down, but the contract is changed from a purchase to a lease; the trade-in amount may be increased, but the purchase price also goes up; or the monthly payment goes down, but the interest rate and length of loan are extended.
Websites with Pricing and Negotiating Tips:
Be sure before you sign!
Unlike some other purchases, there are few remedies for car-buyer's remorse (that is, changing your mind). Contrary to a popular rumor, there is no cooling-off period or statutory right to cancel a vehicle purchase contract, and in fact very few dealers will agree to allow you to cancel. In essence, once you have signed the contract, you have bought the vehicle, even if you haven't yet driven it off the dealer's lot.
Get it in writing.
Price offers, verbal promises and almost any other representations have little or no value if they are not clearly documented in writing. Furthermore, a buyer's order might state that the dealership is not bound by a price quote even if it is written, unless it is signed by a manager rather than a salesman. Also, most contracts state that the dealership is not responsible for any verbal promises or representations not included in the contract itself. Make sure that all such promises, including items or options to be delivered later, are put into the contract before you sign it. This might include floor mats, striping, a stereo/audio system, an alarm system, or special wheels or tires.
Don't buy what you don't want or need.
After the sale price has been negotiated, it's common for a dealer to try to sell you additional options and services (such as paint sealants, additional undercoating, fabric treatments, anti-theft parts, etching, alarm systems and extended warranties). The prices of these items are often highly inflated for dealer profit, so give careful consideration before deciding whether to purchase them. You might also want to do some comparative shopping to be sure that the prices you're being quoted for these items are reasonable. Be especially wary if the dealership tells you that all their cars must have paint sealant or etching applied, or that a service contract can only be obtained at the time of purchase.
Read every document before you sign.
Unfortunately, most people don't follow this advice, but it is the best way to avoid problems, especially concerning the terms of the deal or special promises or considerations.
Get copies of the most important documents before you leave...
...And don't wait for them to be sent by mail. At a minimum, you should ask for copies of your buyer's order or bill of sale, any finance agreement, Warranty Rights Act statement, and an odometer mileage disclosure form.