HOW: Lie on your side. Squeeze your thigh and knee first, in particular, the inside part of your thigh to make your knee straight. While maintaining the squeeze, slowly lift up your leg as high as you can, then slowly lower and repeat.
FEEL: You should feel the muscles on the inside part of your thigh working.
COMPENSATION: Avoid allowing the leg to move forward or back as you elevate the leg, keep the knee straight.