Since the mortgage crisis, banks are careful about who they are approving for loans. Improving your credit will not only help you in home owner ship, but in other areas where credit is important too.
I have helped many people in your situation own their home through a rent-to-own system. We utilize a credit cleaning company to build credit and set aside a portion of each rent payment for down payment. I would suggest looking for lease option or rent to own properties in your area. They are becoming more popular because their are countless people in your situation.
Otherwise I would suggest finding a credit cleaning company, saving for a down payment, and getting a copy of your credit report if you don't know the score. You should start with the credit report. You can get a free one at http://www.freeannualcreditreport.com
You might want to check RateSpeed as well. They offer transparent mortgages so you don't get taken by a crooked mortgage broker. You will see the wholesale rate you qualify for without entering any personal information (no social security number).