While this pose is guaranteed to give you a deep stretch (Visram says it’s the most effective piriformis and gluteus stretch) take it easy the first few times you try it. Going too deep will do more harm than good. “Its important in this pose to stretch within your comfort level,” says Visram.
You’ll know your form is correct if your “hips are level to the floor and square to the front of the mat,” says Visram. When in doubt, “use core strength to keep your torso tall.”
If you find this pose more painful than helpful, don’t force your body into it. Visram suggests trying reclined pigeon pose (laying on your back with your legs in a figure 4 position) to warm up and get your body used to the stretch.