This exercise will help improve flexibility throughout your hip flexors.
Start in half kneeling with your right foot forward and left knee down with the top of your foot flat on the floor. Tuck your pelvis under, shift your weight forward and bring your hands to the inside of your right foot. Hold the stretch for 1-2 minutes and repeat on the other side. You can shift side to side and/or press the top of your foot into the ground to progress the exercise.