We like to use a prop like a bed/couch/massage table/chair to help with this quad stretch. It should be approximately hip height.
Stand with your back against the prop.
Bend your right leg at the knee and place the top of your foot on the prop behind you.
While keeping your upper body perpendicular to the floor, lower into the stretch by bending your left leg. You can use both hand on the prop for support.
While lowering into the stretch, point your knee towards the floor. Try to prevent your knee from moving forward – this will lessen the stretch.