Start with your feet together. Balance on your working leg, with the knee slightly bent.
Begin by hinging at the hips. Maintain a neutral back, and keep the hips and shoulders square throughout the movement. (avoid rotation)
Descend deeper into the hinge, by driving the working leg into the floor, and allow the knee to bend more. Extend the elevated leg out behind you, and keep tension on the glutes and hamstrings. Pause when close to parallel, and you cannot hinge further at the hips. (Do not increase the range of motion by rounding your spine)
Root your foot into the floor, extend your hips and drive your knee through, to return to the start. At the top, squeeze your glutes, core braced & hips fully extended.