One of the main factors that goes into your credit score is your utilization rate, or how much of your available credit you actually use. If you have an available credit line of $10,000, for example, and you carry a balance of $5,000, your utilization rate is 50%. That's not bad, but not great. Keeping your utilization rate below 30% shows lenders that you're a reliable borrower who doesn't max out your cards. A rate of 10% or less is ideal.
This is easier said than done, but reducing the amount that you owe is going to be a far more satisfying achievement than improving your credit score. The first thing you need to do is stop using your credit cards. Use your credit report to make a list of all of your accounts and then go online or check recent statements to determine how much you owe on each account and what interest rate they are charging you. Come up with a payment plan that puts most of your available budget for debt payments towards the highest interest cards first, while maintaining minimum payments on your other accounts.