If you don't know what your credit report says, it's relatively easy to find out. Just visit the websites of Equifax or Trans Union. You can order a copy of your credit report from either of these companies for a reasonable fee.
If there is any incorrect information about you – which isn't uncommon on credit reports – you can request an immediate correction.
If there is derogatory information that isn't a mistake – such as a few late payments – you're entitled to have your side of the story included in your credit report. For example, if you were unemployed for a few months, and that's the reason you were behind on a few bills, then it may be helpful to let lenders know.