Learn how your credit card works
Your credit score loves it when you pay on time. If you're going to be making payments at the last minute (not a good idea), you need to be aware of quirks. For example, the due date on all credit cards means you have until 5 p.m. that day to make your payment (exactly which time zone is up to the issuer). The easiest way to make sure payments are made on time is to set up automatic payments through your online bank or the card issuer's website. Or set an email alert to remind you several days ahead of time.
Knowing little details like that can make the difference between being a responsible credit card owner who makes good use of a credit card, and a credit junkie who ends up nickel-and-diming themselves into the poorhouse.