An efficient fat-burning workout should incorporate the concept of periodization. Periodization involves regularly modifying a parameter (i.e., loads, sets, reps, rest durations, training frequency, exercise tempo, particular exercise, etc.) within your training program in order to continually challenge your body. The purpose is to avoid stagnation in which your body has adapted to the workout and therefore no changes (i.e., increased strength, reduced bodyfat, decreased bodyweight, muscle hypertrophy, etc.) will occur as a result. In other words, you should continually step out of your comfort zone each and every time you train. You have to give your body a reason to get stronger or leaner. It won't happen magically just by working out.
Probably the best way to periodize your workouts is to continually modify the training loads of each exercise. If your goal is to get stronger and leaner, you should gradually increase the loading of each exercise every consecutive workout. For example, if your goal is to perform 8 to 12 repetitions of barbell squats with 200-lbs and you were able to execute 13 reps, then add 5-lbs on the bar the next time you perform this exercise. The modest weight increase will provide enough challenge to your body to cause increased muscular strength and lean body mass (i.e., muscle). The more lean body mass put on your body, the more bodyfat will be burned because one pound of muscle burns about 5 calories per day while resting. This might not seem like much but the caloric expenditure will increase quickly as more pounds of muscle are added to your body. Muscle tissue is much more metabolically active than fat tissue. So the key to burning more bodyfat is to gain more muscle. To gain more muscle you've got to lift heavier weights.
BOTTOM LINE: To lose bodyfat more quickly, be sure to lift heavy weights regularly.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."