Forgot to mention that paying online is a very good thing to do. You avoid the risk of getting slammed with late charges and a punitive APR just because the mail arrived late.

Also, carrying a balance is not per se a bad thing to do. Doing that actually can improve your credit score because the lender is more likely to increase the credit line which helps your debt to limt ratio.

Carrying a high balance is a negative in credit scoring. If you do carry a balance, keep it low most of the time.