Kneel down on the floor with your buttocks on your heels.
Place your hands on your hips and imagine your pelvis as a bucket of water with your index fingers and thumbs running around the top.
Tighten your buttock muscles and abdominal muscles to tuck your tail bone under.
Imagine water in the bucket flowing out of the back.
Next, use the muscles in your lower back to push your tail bone out, arching your lower back.
Imagine the water in the bucket flowing out the front.
Continue this motion, tucking your tail bone under then sticking it out.
Your upper body should remain still and your gaze directly ahead.
Your neutral position is the midway point between the two movements.