Sit on top of your foam roller with your knees bent and your hands resting on the floor behind you. Cross one leg over the other knee, letting your knee drop down to the side to open up through the back of your hip. Roll your pelvis sideways towards the direction that the bent up knee is pointing. Hold yourself on the tight spots and waiting for them to ease. You can roll gently up and down over the gluteal muscles. Do more on the tighter side.
Progressions: Slide your planted foot closer towards you to put the glute that is being rolled onto more stretch.