10. Know the Kelley Blue Book Value
The more knowledge you have, the bigger advantage you have over the dealer. Cars.com and Edmunds.com are two great sites for research, and Kelley Blue Book gives you a solid price quote for what you should be paying for the car. Print out the car value, so when that dickhead dealer tries to tell you that Pontiac G8 is worth $25,000, you can tell him you're not paying higher than $20,000.