The three simplest things you can do to improve your credit score are
1. Never close credit card accounts. And try to make sure that your credit card company never closes it for you. Closing an account has a detrimental effect on your debt to available credit ratio, which is a crucial component of your credit score.
2. Stay away from retail cards. Buy retail purchases with a regular credit card or even better pay cash. Your credit score will thank you.
3. Pay more than the minimum payment and try to reduce your debt load or pay off your credit cards. It will benefit that all important debt to available credit ratio.