A great way to really work your midsection is to perform a core drill. This is highly beneficial because it will force you to go from movement to movement with little rest in between, therefore increasing your body's ability to handle the build-up of lactic acid. Lactic acid is a by product that is created when you are working quite intensely in an ongoing fashion. This does mean however that you must perform the core drill to the very best of your ability or else you likely will not see this benefit.
To start off a core drill, always perform the exercise that uses the larger group of muscles so that you do not fatigue them prematurely. This would include exercises such as burpees and jump squats. Both of these exercises are great to include in your core drill because along with working the abdominal and back muscles, they will also work the quads, hamstrings and hip flexors.
Right after you finish a set of both of those, then drop to the ground and begin a series of crunch exercises. These are even better if you can perform them on an exercise ball as this will reduce your base of support, making you work harder.
After a set of front and side crunches, then flip over onto your back and do ten to fifteen superman exercises. To do these you simply raise the upper body off the floor as high as you can while simultaneously also lifting the legs off the ground. Hold the position in the air for a few seconds and then lower again to complete a rep.
Once that set has been completed then move into a series of leg raises. Begin by lying on your back and keeping the lower back pressed directly into the floor, raise and lower the legs. Be sure however, when performing this exercise that the legs do not completely come down to the ground until the set is complete.
Once it is, rest for a brief period of time and then proceed to move through the entire plan for two or three more cycles.