You know by now that your abs come from core strength, and that includes the front, back, and sides (obliques). Well, today's exercise really works the obliques for those curves in your sides.
From the plank position, rotate to one side. Keep one elbow on the floor, and turn your body so it is facing forward. Stack your feet on top of each other, or put one foot in front of the other. Either way works, but make sure that whatever you choose, you lift the waist high. The higher you lift, the more your obliques are working. Then lift the top arm up.
I know that is not the best description so I hope the pictures help :) If you remember anything here, remember to keep your abs tight and lift your waist up.
Cheers Eights & Weights!