Lie on your side with the leg you want to exercise on top, foot resting on a sturdy platform like a bench.
Support your upper body on your forearm, elbow under your shoulder.
Lift your hips, ensuring your hips are aligned with your body and then lift your lower leg to meet the elevated leg.
This is your starting position.
Then, bend the lowermost hip and bring the knee towards your chest and straighten back to the starting position.
Repeat as advised, then carefully lower your hips to the floor.