To burn more calories throughout your workout you only need to add 30 seconds of cardio. One simple technique I have always used with clients looking to lean up is adding 30 seconds of cardio immediately after their strength training exercise or circuit. Doing so will keep the heart rate elevated thus burning more calories during your workout. If you hate performing boring cardio on a treadmill or elliptical this is another great way to improve your cardiorespiratory conditioning.
For those in better shape add 30 seconds of jumping jacks or jumping rope immediatley after each set of an exercise or circuit. For those beginning their fitness journey start with 30 seconds following only your last set of an exercise or circuit.