HOW: Start by lying on your back. Bend your opposite knee. The first step is to perform a very strong quadricep set by squeezing your thigh as hard as you can. Keeping this constant squeeze, tighten your core muscles and then lift your leg up into the air. Think of making your leg as long and as straight as you can while lifting it. Then slowly lower back down to starting position and repeat.
FEEL: You should feel an entire contraction of the front thigh muscles and your leg working hard.
COMPENSATION: You should not be feeling these exercise exclusively in the front of your hip. If you only feel the muscles in the front of your hip working, it means you are not squeezing your thigh hard enough or you're are not squeezing the quads when you are lifting your leg. Maintaining the thigh squeeze is the most important part of this exercise!