This is the little bit I know of Plank work. Maybe others can add on other ideas.
Plank is the top of a pushup position. It's called a plank because your body is straight and sturdy like a plank of wood. A variation on that is to put your forearms down on the ground like a sphinx, or your forearms still like a sphinx but propped on yoga blocks. Remember to pull your belly button up toward your spine against the pull of gravity. I do an ab series from this sphinx position of bending and straightening the knees several times.
Then there is a pilates move called "Leg Pull" that you can do from the full plank or the modified sphinx version. Lift your right leg off the floor to a distance where your hip doesn't rotate up, nor does the position of your spine change. Rock back on your left heel (like stretching your calf), rock forward on your toe (like a calf raise) the lower the right leg to the floor. All of that is done with NO torso movement. Switch legs and repeat the series 5-10 times slowly on each leg.
I'm sure there's lots more to do from this position. I'd love to get some new ideas.