If you have balances on more than one card, list out each card’s balance, credit limit, interest rate, and minimum payment. Keep sending the minimum balance to each, but pay whatever extra money you can toward the card with the highest interest rate. (That will help you pay less interest over the long run.)

Call the phone number on the back of each card. When you get connected to a customer service representative, tell them you’d like your interest rate lowered. If you have a good record with the company and haven’t already had your rate lowered in the last six months, there’s a good chance they’ll offer you a lower rate. Even a few percentage points can save you hundreds while you pay the card off. All it takes is five minutes of your time.

Credit cards can be a great tool, but it takes discipline to make them work for you.

Start by using just one credit card—hopefully one that offers rewards. Use it for daily expenses and other planned purchases. Along with this, stick to one unbreakable rule: The card must be paid off in full every month. Once this is no longer a struggle and you aren’t tempted to overspend, you’ll know you’ve mastered credit cards.

As you pay off each card, it might seem like a good idea to close the account so you aren’t tempted in the future. Watch out! Doing that can temporarily lower your credit score. Your score depends partly on how much of your available credit you’re using. Closing accounts can wreck that ratio.

Instead, take the cards out of your wallet and put them somewhere safe. (Some people freeze theirs in ice to make them hard to get to.) To keep the cards active, use each one once a year and pay it off right away.

Your oldest credit card can be especially important. It shows a longer credit history, which can help raise your score. You definitely want to keep that card active. If the card has an annual fee, a high interest rate, or some other feature you don’t like, contact the card company and ask to have the fee waived or the rate lowered. If that doesn’t work, just wait until you have a better card with seven to ten years of history, and cancel the first card.