Make a list of different auto loan lenders and their interest rates and terms, before you go to the dealer (the web is usually the easiest way to do that). Did you know dealers get a commission on the loans they refer? If you’re not careful, that extra bit of money for the lender could mean you pay a higher rate than you would if you got the loan yourself.*

Get a credit report and figure out your FICO scores. Removing any incorrect negative information from your report will help you get a better deal. Knowing exactly what your score is will help you figure out what interest rate you can realistically get.
Have bad credit? Try going to your credit union, bank or another institution where you have a relationship. Lenders like to help out established customers. If your bank still won’t help, online "bad credit auto loan" lenders usually offer better less expensive loans than dealers who advertise their great deals for people with poor credit.
Use a vehicle loan calculator. It will tell you what your loan will cost each month. It saves you the time of looking at vehicles you can’t afford, makes you aware of what information you’ll need to apply for a loan, and is a "reality check" of your financial condition.
Comparison shop, comparison shop, comparison shop. You don’t get the least expensive car by choosing a dealer at random, and you won’t get the least expensive auto loan that way, either.
Start researching your options now:
Get credit reports and FICO scores here
Use this vehicle loan calculator
Comparison shop among these lenders