As for boosting scores - there are probably several reasons that your scores are down - the main things that I see on credit bureaus with sub-600 borrowers are:
1. Revolving credit balances that are over half of the cards' limit. If you have a Sears card with a limit of $1000 and a balance of $800 you aren't doing yourself any favors - it would be much better if you carried a balance at $300 or below.
2. Collections or judgments are typical to drag a score down. If there is inaccurate information on your report, you can take the time to get things fixed or you can even pay a professional to make these thing happen if you do not feel that you can take the time to do it yourself.
Hope this helps!