Improving credit rating?

I went online and viewed my credit report. I knew it would be low because I went through a bankruptcy about 4 years ago. I found out that I had several credit card sitting at a zero balance that I hadn’t used in years. I guess potential debt effect your credit negatively as well. But there are a few things on there that I don’t have a clue what they are. I think they were turned over to bill collectors and that’s why I don’t recognize the names…..one was "American Capital Ent.". I haven’t the foggiest what that is. How can I improve my credit score? It’s right at 600.

I would suggest you try to contact the agency where you got your rating from.