If you want to burn fat while building muscle, circuit training is the most effective method. Try using full body exercises that are compound movements and will be more effective...try deadlifts, squats, olympic lifts, pushups, and pullups. Aim to get your heart rate up pretty high while you do the lifts and stack 3 to 4 exercises in a row. In between circuits you can rest for a minute or two, but this time should decrease as you get in better shape. The key is to work hard for each circuit as a way to improve both your muscular strength, power, and endurance.