If you're applying for an auto loan, you should check your credit score before you make an application.
First of all, you need to know what your chance is of being accepted. If you have low income and a low credit score, you may not get a car loan at all. If your credit score is only moderate, you may find you have to apply for a loan at higher interest rates than someone with a better credit score.
If your credit score is not that great and you can put off your car purchase by six months, then you could clean up your credit score before you apply for an auto loan. Paying all your bills before the due date, reducing your credit card balances outstanding, and checking your credit score for any errors, can all help to improve your credit score before you apply and make it more likely you will get the loan you want.
Even if you have a good credit score, you may be able to improve it - check your credit record and query anything you think is wrong. For instance if you closed a loan account after paying it off, it should be recorded as 'paid in full' - make sure that is the case. Your care and attention could be rewarded by a cheaper interest rate on your auto loan.
If you have a poor credit score (below 680) you may have to play clever to get an auto loan. Different dealers have different policies on granting auto loans, so you should aim to find a dealer prepared to make you a loan before you settle on a brand or model of car.
If you have a good credit score, you may find that the cheapest auto loans are not those provided by dealers, but by independent auto loan web sites. These can save you as much as a thousand dollars over the life of the loan. In any case, whatever your credit score, you should check on the internet to see what rates are being offered. Then if a dealership attempts to sell you an expensive loan, you will know you aren't being offered the best deal - and you'll be able to query it.