Here's a few ways to improve and keep a good credit score.
Don't Open too many credit cards.
Only open credit card accounts that you are sure you can pay off the balances.
Having too many credit cards open with high balances can destroy your credit and applying for too many credit card accounts can harm your credit score as well.
When you apply for credit or a loan you have a hard inquiry put on your credit rating. This can lower your credit score.
Pay off your credit card balances as soon as possible.
When using credit cards don't spend your whole credit card limit unless you know you can pay the credit card balance off in full.
Paying off the full credit card balance as soon as possible after using the credit card can improve your credit score.
If you only pay the minimum payment you won't get the balance paid off soon enough as the minimum payment will mostly cover the interest rate.
Pay off any debt you have.
If you have any outstanding debt such as student loans, personal loans etc then do your best to get hose paid off as soon as possible.