Q. What should I do with cards that I don’t use? Should I leave them open or close them?

A. Close the account and destroy the card. That’s the safest way to avoid fraud and identity theft. But first there are factors to weigh.

Best case: You should be using no more than half your available credit at any time, because your debt-to–available credit ratio accounts for about 30 percent of your credit score. If this ratio would be affected, you may be better off keeping the account open until you’ve paid off your debt.

A lengthy credit history also bolsters your credit score, so if you decide to purge some cards, “cancel in order of the newest card first,” advises Robert D. Manning, Ph.D., director of the Center for Consumer Financial Services, at the Rochester Institute of Technology, in New York.

Q. I may be late with a credit-card payment. What should I do?

A. Call your bank—it might waive a late fee for a good customer. If you have a day or so before the payment is due, pay by phone or even overnight the check. That’s “usually cheaper than the late fee,” says Ellen Cannon, editor of Bankrate.com, which offers financial-rate data.

The best strategy: Pay your bill on time, in full — even if your bank doesn’t like it. “In the industry, people who don’t carry a balance are called deadbeats,” says Cannon, “because they’ll never make money on you.” A smart way (for you) to do business.