HOW: Using some sort of elevated surface like a box or bench, place the side you want to target on the box. Place the inside part of your knee on this surface, use something soft for padding if you'd like. Lift your hips in the air by driving the inside part of your knee downward into the box. After lifting your hips up, lower yourself back down to the floor slowly and repeat.
FEEL: You should feel all the muscles on the inside part of your thigh working, in particular, your groin region. You will also feel your core and shoulder muscles working.
COMPENSATION: Keep your hips stacked on top of each other, do not rotate them forward or back. Put your elbow directly below your shoulder.