Shopping around can save you thousands on the life of the loan. Don't just go with the dealer's financing plan.
No. 1: Details matter
You know when you go in for a car loan and they shove the stack of papers under your nose and you just sign on the line, grab the keys, and go on your merry way? Yeah.
Don't do that. Not that any lender would be willingly shady, but a detail you may think exists in fact may not.
Know all the details of your deal. For instance, what's your interest rate? Can you afford it? Is there a fee for prepayment? What's the grace period for payments? How will you get the title when the car is paid off?
Think also about warranties. What will the warranty cover? Is there something that would destroy you, financially, if it broke and your warranty doesn't cover? If so, you might want to renegotiate the terms of the warranty or start saving up for a rainy day.