Jones recommends glute bridge holds also known as "isometric glute bridges." She says they're useful for engageing the glutes.
Lie on your back with your knees bent and feet flat on the floor. Be sure to keep your feet underneath your knees, not in front. Plant your palms by each side, facing down.
Press through your heels to raise your hips up to the ceiling, tensing your abs and squeezing your butt as you do. You should be making a long diagonal line with your body from your shoulders to your knees.
Make sure your spine doesn't round and your hips don't sag. Keep your abs and butt muscles engaged.