Understand the basics of credit scoring

You need to know that the two most important factors in your scores are:

• Whether you pay your bills on time.

• How much of your available credit you actually use.

It's essential that you pay all your bills on time, all the time. Set up automatic payments or reminder systems so that you're never, ever late. All it takes is a single missed payment to trash your credit scores -- and it can take seven years for the effects to completely disappear.
You also don't want to max out any of your credit cards, or even get close. Keeping your credit use to less than 30% of your credit limits (10% is better) will help you get the best possible credit scores -- and should help keep you from getting over your head in debt, as well.
Finally, you don't need to carry a balance on a credit card to have good credit scores. Paying your bill in full each month is the best way to keep your finances in shape and build your credit at the same time.