Here is a great site I've used to help prepare for my last two new car buying experiences. If you are going a dealership for any vehicle, new or used you owe it to yourself to study it thoroughly.
http://www.carbuyingtips.com/Over the years I have worked to perfect my car buying techniques taught to me by my father who used to sell cars himself in the 1950s and then worked for years as an auto insurance adjuster/investigator. My wife and I tag team the salesmen and work them over, sometimes to a lather. One time when we picked up our new car I asked the salesman if he wanted me to send him referrences and he actually said "From you? No way!" That was the same guy that actually said that I was taking food out of his childrens mouth.
Some of rules of thumb to get a better deal.
Stumpy's laws of car buying from a Dealer.
READ EVERYTHING (and understand it, bring a calculator)
Sell your old car yourself. You'll make much more than trading it in and it takes out another way that the salesman can screw you. One less thing to negotiate.
Do your research. You need to find out how much they are paying for the vehicle or damn close to it in order to make an offer that is reasonable to you and allows the dealer a fair profit. It's OK for them to make money but not rip you off. Have them take off BS mark-up items like "Dealer Prep", "Advertising Fee" etc.
READ EVERYTHING If you have to finance , what they offer at the dealer is not always the best you can do especially if your credit is poor. Again, do your research. If necessary find your own financing. Also you've eliminated yet another way they can screw you by playing with the numbers.
Watch for dealer incentives (rebates) and manufacturer financing. Be aware that the the dealer may be getting manufacturer kickbacks and remember to include this to lower your offer.
READ EVERYTHING Don't impulse buy Test drive and make your car decision BEFORE going in to negotiate. Make sure you know exactly what car you want, and have already taken into account the costs of options.
Fully testdrive (including freeway miles) the same vehicle that you are purchasing and do not let them switch vehicles. Compare VINs if necessary.
READ EVERYTHING Don't buy options you don't need. And don't let them talk you into it. Do you really need extended warrantees, rustproofing (If you must have it check a local body shop to do it) Also don't buy dealer accessories, those things can be found for much cheaper and often way better quality somewhere else. (One time after I had negotiated a deal, I came to pick up the car and noticed they had added mudflaps.$250 mudflaps at that. I told them to take them off and then they tried to charge me for the labor to take them off. I told them "go get a screwdriver and I'll do it." They finally removed them.)
Don't fall in love with any car . There are other cars and other dealers. No matter how long it takes, and how much time you've blown be prepared to walk at any time if they can't be reasonable. Believe me, you walk after two hours of negotiating the salesmans going to be much more pissed off than you are. You have ALL the power here. The salesman and the dealer have no power if you don't give it to them. Don't forget that.
Try to stay away from overly popular, trendy or rare vehicles to get the best prices.
Oh did I mention
READ EVERYTHING ?
Oh one more thing. If you can't afford at least 20% down on the vehicle you shouldn't be buying. 20% down is really the minimum to make sure that if the vehicle is totalled you don't end up being upside down on the loan and owing money on a dead car.