When you've had past financial problems using a car loan to rebuild your credit can be a great part of an overall financial plan.
If your ultimate goal is credit improvement than before anything else you'll want to get a copy of your credit report and look it over. Are there any past mistakes, either yours or someone elses, on your report? If companies have reported things incorrectly make sure to contact them in writing to get them changed. Things you'll want to look for include overdue accounts that you've paid off, or the limit on your cards. If they've marked the limit on your cards as lower than it is you'll want to have that fixed because one of the factors used in calculating your score is the amount of credit available to you versus the amount you've used.
If there are any things from your past, like overdue payments, that need to be paid off now is the time to take care of that.
You're not only fixing these past problems to improve your credit overall, but to get your finances to look better for your car loan application. The better your history, the better interest rate you'll be offered.
If your score is in really bad shape and you have a hard time finding approval to get a vehicle then start off cleaning things up as mentioned above and then work on building some new history with a secured credit card. You can get one of these at your bank or most other financial companies. You deposit a few hundred dollars into a savings account which will work as collateral for the card and set your limit. Use this card lightly and pay it off in full each month to build up a history of positive use that you can show a potential lender.
Once you've done these things apply to get auto financing which will give you a history of positive installment payments. Make sure you pay on time each month to build up this good history you're working so hard for. Using a car loan to rebuild your credit is one of the best ways you can go about building up a positive history.