2 Sets of 12-15 reps at each height
These can be done from three different positions: low, middle, and high. I suggest a mixture of all three. If you do it from the top, the movement should mimic a sledgehammer swing. Put the cable at the midpoint and make sure your feet are wide so you only engage your upper body. A top-to-bottom cable twist should mimic a bad golf swing.
Each of these variations provide rotational, concentric abdominal work which engages your entire midsection, including the obliques. Make the movement fast and powerful. Go for speed.
2. Overhead Medicine Ball Slam
3 Sets to failure
This is full body movement requires energy generated from the core. Raise a medicine ball above your head with both arms and throw it down as hard as you can. Pick it up and repeat until you are fully exhausted.
3. Planks
2 Sets of 30 seconds
During each training session, your goal should be to increase the time you can hold a plank position. Have a partner assist you once you can hold a plank for more than 20 seconds; have your partner push you down or place weight on your back.
4. AB Roller
3 Sets of as many reps as possible
I like the ab wheel because it can be scaled to skill level. Start on your knees so you can limit the amount of extension. The extension portion should be slow and controlled. As your strength increases, try doing them from a standing position.