Use what you have at home.
Like Kirsten King from Fluidform demonstrates, all you need is a chair and a small exercise ball. If you don't have a ball, a small pillow or a rolled-up towel will work, just get something behind the knee you can actively squeeze. Be sure to keep your standing leg bent to help feel it in your glutes even more. Kirsten recommends trying this exercise daily for 15 days, with repeat 30 reps on each leg 3 times.