Sure, it takes months to make a significant improvement to your credit rating but there are some surefire ways to speed up the process. Here's a few lesser known tips:
1. Become an authorized user on someone's account who has a high score. You don't need access to their account, they don't need to give you a card, they just add you as a user and BAM, within weeks you will see a bump.
2. Review your report regularly, which is free at https://www.annualcreditreport.com/index.action and look for anything you can dispute to repair your rating. Often if you contact the reporting business and explain your circumstances, they may be willing to help you clear up some past negative dings on your report.
3. Always pay at least the min. every month on every account but if possible pay the balance in full. Late payments are the FICO killers. Along with that, having a healthy ratio of credit available to debt incurred makes a difference. Try to stay under 30% utilization of your total available credit. Call to increase your credit line on existing accounts but again, don't carry a balance of more than 30%. Banks like to lend money to people who don't need it.
4. Carry a variety of credit types. A mixture of mortgage, auto loans, personal loans and revolving credit accounts increase your overall score.
5. Never close an old credit card account. Credit history makes up a nice piece of your score and the longer you've had an account open, all the better. Closing an account will also lower the total available credit to you. The only time I would close an account is if the card benefits were not worth the annual fee. Before you close a card, call the bank and ask for a retention offer or for a product change to a no annual fee card.
6. Experian, one of the 3 major reporting agencies has a new program called Experian Boost that allows you to receive credit for paying your recurring bills every month. These can include your Utilities, Internet, Netflix and so on.