There are two popular methods that people use to tackle debt.
The first is to concentrate on paying off the debt with the smallest balance first (never forgetting to make required payments to all debts, of course). After that balance is repaid, you can then apply that payment to the card with the next smallest balance and continue the process until all debts are satisfied. This method can be very rewarding because you see progress quickly.
The second popular method is to first concentrate on repaying the debt with the highest interest rate. This method will save you the most in interest charges over time. Regardless of the method you choose, be patient and persistent.