Start on the floor, resting on your forearms and knees.
Step your feet out one at a time, coming into a plank position.
Contract your abs to prevent your booty from sticking up or sinking. Your spine should be parallel to the floor, with your abs pulling toward the ceiling.
Hold for as long as you can. Aim for 20 to 30 seconds in the beginning, and work your way up to one minute as you get stronger.