NEW YORK (MarketWatch) -- It's a great time to buy a car, but applying for a car loan is one of those occasions when your credit record matters most. You have great scores? Car loans are cheap, and carmakers are eager to deal. Bad score? You'll pay and pay.

MSN Money columnist Liz Pulliam Weston reports that if you plan to get a car loan this year, you're likely to find a warm welcome from car dealers and manufacturers, who are increasingly desperate to revive sagging sales -- but only if you have untarnished credit. If you have troubled credit, you'll find higher rates, increased scrutiny and warier lenders, but still won't face anything like the trouble you'd experience if you were shopping for a mortgage.

Some lenders, though, can vary from moment to moment, offering a 0% rate as long as you qualify for any financing one month, and giving that same rate only to those with the best credit the next.

So how can you make sure you get the best possible deal? Weston suggests this four-point strategy:

1. Do your homework. Research cars and current incentives, such as low-rate financing, cash back or leasing deals, using sites such as Edmunds.com, Cars.com and Consumer Reports. (CR offers unlimited new-car reports, which include detailed pricing information and reviews, for $39.) Although manufacturers are offering some eye-popping deals on leases right now, keep in mind that buying and keeping your car for 10 years or more makes the most financial sense.
2. Figure out what you can really afford. No car is a bargain if it upends your financial life. Don't finance a car for more than four years, try to put 20% down to make sure you always have some equity in the vehicle and be wary of payments that eat up more than 10% of your income.
3. Get approved elsewhere for the loan. Credit unions, banks and online sites such as E-Loan (www.eloan.com) typically offer the best rates. Applying for a loan doesn't mean you have to take the money, but it does lock in a rate that you can then take to the dealership. It helps you get an idea of your market value.
4. Ask the dealership to beat the rate. You'll want to first negotiate all other aspects of the deal, including the price of the car and the value of your trade-in. Only then do you bring out your lender's rate and ask the dealership to do better. The dealership often has access to a slightly better wholesale rate that could knock a quarter of a percentage point off your rate. If so, you can take the dealer financing; if not, go to the lender that has already approved you and get a cashier's check to buy the car.