Anyways, this pose is super simple if you just look at the picture. But to get maximum stretch in your butt and your hip flexor (trust me you will!), then I would try to make the right leg in the picture more perpendicular. Do this slowly as it will activate the stretch in your right glute extremely quickly. Once you get to this point, it is easier on the back and will provide more of a stretch if you lay your stomach over your leg and stretch your arms out in front of you. If you feel your leg moving a lot (the left leg in this picture), then press flex your foot and use your toes in the ground to push your body into a sturdy position. If you hold this you will also activate more of a stretch in the hip flexor.
I love this pose. After a day of running or a golf tournament, I always do this one to release tension.
Have you ever tried this pose before? Does it hurt your body a lot like it used to kill mine?