Okay, so I'm bitter. I've worked hard for 10 years in order to pull my credit rating all the way up to "questionable", and still can't get a mortgage. But action sweetens bitterness, so I'm passing on a really fantastic tip.
You should get a copy of your credit report. These things are often inaccurate.
Furthermore, you don't have to sign up for some hokey "credit protection service" to get one. You don't even have to apply for a credit card. Many states have laws entitling you to a free copy once a year. When you get your credit report, you can ask the agency to research any inaccuracies, and get them removed.
Colorado, Georgia, Massachusetts, Maryland, New Jersey, and Vermont let you get a free credit report once a year (twice in Georgia).
All other states let the agencies charge you. Some even let them charge you sales tax. If you live in such a state, you may want to write your state government people about this. (charging you money for crucial information about your own self... Bah.)
Here's how to get your credit report from the three major agencies:
That is all.