Stand in front of an elevated surface, and putting your right leg back, rest your toes on the surface. Avoid resting on anything too high or too low, as this can cause strain.
Slowly bend your left knee until your hamstring is parallel to the floor, making sure to squeeze the glutes throughout the move. You should also lower your pelvis and ensure that your left foot is far enough forward so it is just above your ankle.
Straighten out your bent left leg (still elevated) while returning to the original start position. Complete your reps, then repeat with the opposite leg.