Lock your ribs down with your abs and tuck your tailbone under.
Step back onto the bench while keeping your pelvis square.
Space your feet so that at the bottom position your forward knee is at about 90 degrees, your forward shin is vertical and the trailing leg knee is just off the ground and slightly behind your hips. Your ankle should rest on the edge of the bench.
Don’t let your pelvis roll open as you lower to the bottom position.