Pay things off, that's the first step. After everything is paid off, it really just takes time. Things that can help you: If you don't already have a CC of some sort, get a secured CC, like through a bank or credit union. You'll have to put down a security deposit, and whatever you put down is your "limit".
Also, car loans, or anything with installment payments can help 'build' your score up, but ultimately it just takes time for things to fall off. Also, try and keep your credit utilization under 33%. That means if you have a $10k limit on a CC, don't charge more than $3300/month very often.
Creditors want to see good payment history, so paying things that are past due, and keeping things current are very important. Try getting like a store CC or a gas card. Most store CC's offer 0% for a certain time, split the amount up over that period and pay each month, this shows you can keep track and do so on time.
good luck man, my wife went through the same thing a few years ago, we're still dealing with stupid shit from it, but she has a car loan in her name at a very good rate now, and her secured CC changes over to a regular CC here shortly, it does after one year of good standing.