STARTING POSITION:
Get in a hip extension machine. Select the appropriate resistance on the weight stack. If you want to start with your right leg, the weight stack should be at your right side. The beginning of the arm of the machine should be at your hip high, if not adjust the machine to get it. Rest your right leg on the pad. It should be under your thigh just behind your knee. Your hip should be at 90º, if it's not, adjust the machine to get it. Contract your pelvic floor and core while keeping your chest up. Grab the hand bars firmly.
MOVEMENT:
Extend your right hip and knee while you exhale. Make sure you only move your right leg. Return to the starting postion with a smooth movement, preventing moving weights from touching the rest of the stack. Repeat the movement for the specified amount of repetitions and then switch sides and repeat with the other leg.
TIPS: The exercise key is quality over quantity. The trick is to perform the exercise using proper form.