Burn fat fast by going all out!
To burn optimal body fat, your workout needs to be intense and you need to work the entire body. Working one muscle at a time will make it extremely difficult to get a nice, flat stomach. Why? - Because you're not utilizing your body's full capability to burn fat.
If you hit the whole body with big compound movements, you'll be seeing your belly disappear a lot faster. Do exercises that work a bunch of muscles at once. It's all about the "after effect" that your workout will have on your metabolism that will get you results. The more intense workout you do by hitting as many muscles as possible during the workout will ensure that you get your metabolism cranking to higher levels, leading to greater fat loss during the rest of the day and long after you're done training. Larger muscle groups like the legs and back, tend to require more energy and therefore, burn more fat. Increase your intensity even further by minimizing or eliminating your rest time and try alternating between a larger muscle group exercise followed by a smaller one. Your smaller muscle group exercise could be considered your active recovery, thereby increasing the quality of your overall training time as well as revving your metabolism.
-With notes from Dan Grant