Paying down debt may be the single quickest thing you can do to improve your credit score. Thirty percent of your score is determined by how you use your debt. If you have a lot of credit available to you, that is usually a good thing because it shows that lenders view you as responsible. However, if you use all of that credit, then it becomes a bad thing. Lenders may be afraid that you are living beyond your means, or that you will be unable to juggle all of your debt payments.
Typically, you should try to keep your usage of credit to 30 percent or less of your available credit. That means if you have a $100 credit line, you should charge no more then $30 on that card. If you have already maxed out or charged more than that on a credit card, paying off that debt and lowering your debt to credit ratio can result in a big improvement in your credit score.