Just like the Bermuda Triangle, or where Amelia Earhart went, or the success of Mischa Barton’s “acting career”, credit cards can be a big mystery. You don’t want to screw yourself (and your credit score) over by making dumb mistakes, but if you’re smart about it they can really help you out when money is tight.

Here are some tips I found at MSN Money’s 5-Minute Guide to Credit Cards…

1. Pay Off Your Balance Every Month

This seems like a no-brainer, but it’s just so easy to mess up. Every time you don’t pay off your balance you’re paying late fees interest. That’s how credit card companies make money. Sure it takes a bit of discipline to pay it off totally each month, but you’re really only screwing yourself over if you don’t.Even one late payment can trigger companies to raise your interest rate. Even worse, late and missed payments lower your credit score and make it harder for you to get a good interest rate on future credit cards and other loans. Like a mortgage. Did you really want to rent or live with Mommy and Daddy forever? No, we didn’t think so.

2. Limit The Number Of Cards You Have

Experts say between two and six is good. If you have fifteen, you’re doing something wrong. Applying for lots of cards at one time can hurt you credit score, so don’t go buck wild and send in for every card you can think of. Do a little bit of online research, pick a card or two that you really want and only apply for those. On the other hand, closing too many credit card accounts at one time will also lower your score. Think moderation.

3. Read the Fine Print

Sure, the tiny legal stuff at the bottom is boring and it’s fun to pretend none of that stuff will affect you, but if you’re old enough to have a credit card you’re old enough to suck it up and make sure you know all the details. Find out the interest rate you’ll be charged, the grace period for paying your debt off before interest kicks in, and your credit limit.

4. 30%

Paying off your balance each month is smart for you because it saves you cash and interest charges. Credit bureaus, though, don’t care if you pay it off each month. They care about how much of your credit you use. If it’s excessive, that shows that you can’t control your spending and your score will drop. Experts say don’t use more than 30% of your limit on each card and you’ll be cool.