Do: Lie on your side with your legs stacked and your head resting on your arm. Tighten the muscle in the front of the top thigh and lift that leg into the air. Hold for one count, lower to touch the bottom leg and then lift again. You can also use ankle weights or a resistance band.
Don't: Matthews says she often sees clients curved into the letter C, with their feet and torso creeping forward from the hinge of their hips. Stay straight from your head to your toes. Also resist lifting your top leg way up in the air. "There are no bonus points for extra height," says Matthews. (After about 45 degrees, the hip is no longer the focus, and other muscles take over.)