The key to rebuilding credit is to let creditors know that you are responsible. Responsibility involves making scheduled payments on time, all the time. That often means establishing a budget and sticking to it.
If you are ever late with a payment, call your creditors and apologize, let them know it slipped your mind and sometimes, you may even get them to wave the late fee.
Do not treat creditors like the enemy.
Remember this is their money you are using. The right kind of attitude will help you rebuild your goals.