To get into the side plank position:
Lie on side. Stack top foot on top of bottom foot. Push up into a side plank.
Now, squeeze the medial glute (side of hip) to raise leg as high as you can. Lower leg back down in a controlled manner. Repeat.
Perform 1-5 sets of 8-12 reps per leg. Or, perform 1-5 sets of 20-40 second intervals (doing as many reps as possible during those intervals).