It is fairly simple to keep credit score improving. First thing to keep in mind that your credit worthyness depends upon only few main factors. Paying your bills on time is the most important one. There are few other factors involved. Below are the factors, following which would help to improve your credit score a lot.

1. Make sure that you pay your bills on time. Paying bill on time does not do much, but a failed one adds a lot to the negative side.
2. Pay off your credit cards. Paying off credit card balance in full always adds positive value too your credit history.
3. You have to try to keep recurring credit balances as low as possible.
4. Get a local store credit card. They offer very low credit, but eventually they would help you to improve credit score.
5. Find a close friend or relative to co-sign your credit card. This will not affect their credit but it will improve your credit significantly.
6. Get Secured credit card. You could do that using some Home Equity line products or by submitting some security.
7. Closing un-used credit cards would not do any favor. But using them from time to time would make sure that the lender would update your credit bureau record.
8. Do not let your credit reach the limit of your card. It is a good idea to keep them well below 50% of your credit limit.
9. Plan ahead when you go for credit. Do not use them all the time for big ticket items.
10. Go to debt managing page for further information.