Stand on one of your legs, one knee touching the other. You can hold a chair or the wall to keep you steady if needed.
Grab your foot, using your hands, and pull it towards your butt. Be sure to push your chest up and hips forward. Try not to worry about pushing your foot too close to your backside; your focus should be on feeling the stretch in your quad muscle and pushing your hips forward to get a good hip flexor stretch.