When you have the money to pay off or pay down one of your loans ahead of time, choose the one with the highest interest rate. It's costing you more every month than loans with lower rates. If you have both government and private loans, pay off the private loans first. They often have higher rates and less flexible repayment options than government loans.
Get familiar with your loan documents. Some lenders -- though not most -- charge a penalty for paying loans off early. And many lenders require you to request that extra payments be put toward the principal, which will reduce your overall interest payments. With some loans, extra funds are automatically put toward future payments unless specified otherwise.