You should have two concerns with your credit cards. (1) Not paying any more interest (2) Improving your credit scores.
If you start paying the balance listed at the end of every statement (pay in full or PIF), then you won't be paying any more interest. And in a couple months, that will cause all CCs except the ones your using to have a true balance of $0.
The goal should be to get all your CC's to have a balance of $0 and then keep the balance of the remaining one to be always greater than $2 and less than 9% of that card's credit limit. That's the received wisdom in terms of getting the most FICO juice from your CC's. And even that is not something you need to do except in the 2-3 months before making a major purchase (mortgage pre-approval, closing on a house, buying a car, etc.). If you PIF every month and make sure you are always spending a good deal less than you make, you should be fine.
Your auto and student loan will be great additions to your credit mix, btw.
