HOW: Place your forearms on the ground with your elbows straight under your shoulders, your knees straight down from your hips. From this position, move one leg up while the knee stays bent. Act like you're trying to drive your heel towards the ceiling. Bring it back to the starting position and repeat.
FEEL: You should feel you glute muscles working. You should also feel your core working.
COMPENSATION: Don’t twist your back as you bring your leg up. Keep the knee bent as you bring it back.