Remember that a bad credit score can cost you thousands of dollars in high interest fee so it is in your interest to aim for the highest possible credit score. 

The first thing you need to do is to actually obtain your credit reports which credit agencies have an obligation to supply you with and carefully analyze the items it contains.  If you feel that an information is inaccurately reported, you are entitled under federal law to challenge the said information and have it removed, should it indeed prove to be inaccurate.