Pigeon pose is a common yoga pose for both the piriformis muscle and the hip flexors. It is often used to help treat sciatica.
Start by laying on your stomach on a comfortable surface such as a yoga mat.
Inhale as you use your hands to press your chest and hips upward off of the floor. While you are here, bring your right knee up towards your chest and let it rest on the mat towards your right hand. Your foot should be positioned towards your left hand. Exhale as you lean your chest forward until you feel a stretch in your right hip. Hold for 30-60 seconds. Repeat 2-3 sets total on each side.