I have a few suggestions for you, don't know exactly what your credit situation is and I'm not asking you to disclose everything here. However, I have been rather successful in rebuilding my credit after two forclosures, two charged off cards and a defaulted car loan as well as loads of medical collections. While my credit is far from perfect in the space of a few years, I've been able to rebuild my scores in the low 400s to now high 600 and low 700 range. So without further ado, here are my suggestions for your credit.
If you don't have any credit cards... get some, and learn to manage them properly, it's not hard really. Fico likes to see a balance to limit ratio of 30 % or less. Although under 10 % is best.
Moving on if you already do have a couple cards, keep your balances low! Seriously, it's that important. For example, I payed off my cards with my tax return and enjoyed an instant 50 to 70 point jump in my scores!
Next thing. Pay your bill on time every month. Simple enough, and this is roughly 30% of your score.
Finally. Don't be afraid to use a credit repair company if you have some questionable info on your report. Most reports contain errors. I used on for about 6 months last year and they really did clean things up a bit!
I hope these help. Feel free to message me or shoot a text or call if you would like any more input.
Disclosure: I am not any attorney nor am I affiliated with an attorney or credit repair agency. The above suggestions are only my experiences of things that have worked for me and not intended to substitute legal or financial advice from a qualified professional.
Happy Investing!