Credit scores can get low for a number of reasons, such as a poor debt-to-income ratio, late payments, or exceeding a limit. As the saying goes, if you're in a hole the first thing you do is stop digging. The key to repairing a low credit score is learning what factors are bringing it down, and take all the steps necessary to turn those around. Once you do that, you have to start managing your credit responsibly so it doesn't go back down.
Request a free credit report from Equifax, Experian, and Transunion, which are the three major credit reporting bureaus. There is no way to fix a problem with your credit report if you have no idea what it is, and the only way to know is to have copies of your credit report from all the major sources.
Examine your credit report in detail to see what factors are hurting your score. Each bureau uses a different mathematical formula to calculate your score, so the scores may vary depending on which category is rated poor. Look for any errors in their data. If a payment was reported late, check your records to see if it's accurate. If there are any balances that are reported higher than they really are, that needs to be corrected. There may even be whole line of credit that is counted when it doesn't exist, or a good line of credit you have open that isn't taken into consideration.
Submit an official dispute of any errors on your credit report with the bureau, and report the allegedly false information. Include any details and documentation that you can. The bureau should acknowledge receipt of the information, and send you a new credit report that reflects the changes.
Increase your income with a different job, an additional part-time job, or a side business. Not only will this give you some much needed breathing room between your income and expenses, it will improve your debt-to-income ratio. The added income will help you pay all your bills on time, and maybe even pay them down faster than before. Reducing the amount of credit you're using will also improve your score.
Lower your expenses by living a less expensive lifestyle. Downsize your home to lower housing costs, get a cheaper car to lower your monthly transportation costs. Eliminate any unnecessary monthly expenses. Remember that it is only a temporary lifestyle change while you reduce your debt and repair your score.
Create a monthly payment reminder through your online banking program or through software on your computer. This will help ensure that you will make timely payments in the future.