To increase the internal range of motion in your hips you should do strengthening exercises three days a week and stretch daily. Tight muscles make it difficult for the hip joint to move, and weak muscles will not be able to move the hip very far. Consistent exercises will fix this problem and allow you to rotate your hip freely.
Using just your body weight or a resistance band while rotating your hips inward will strengthen your internal hip rotator muscles. Stand on your right leg with your hand against a wall or chair for balance. Bend your left knee and lift your leg into the air. Pull your knee back as far as you can and then rotate your hip inward. Do hip circles with your left leg and then do the same for your right leg. Start with five per direction and work up to 10.
For more of a challenge, wrap a resistance band around your left ankle as you stand on your right leg. Attach the cable to a stationary object behind you at floor height. Do hip circles against the resistance of the cable. Do the same on the other leg.
Tight external rotator muscles will decrease the range of motion of the internal rotator muscles. The Z stretch, a modified version of the hurdler's stretch, is an excellent hip opener to stretch these external muscles and increase range of motion. Sit up with the bottoms of your feet together and your knees open. Rotate your right hip outward so the inside of your right knee touches the floor. Allow the outside of your left knee to touch the floor. Hold this position for two to three minutes, if possible, and then switch the positions of your legs. After holding this side for three minutes, switch your legs back. Hold each side three times.
The piriformis is an external hip rotator that can easily become tight and inhibit the range of motion of your hips. Stretching and loosening the piriformis muscles will increase the internal range of motion of the hips. There are a few ways to stretch the piriformis muscle, but the easiest way is to sit up straight with your legs extended in front of you. Bend your left leg and cross it above your knee. Grab your left ankle and pull it toward your left shoulder. Keep both sides of your buttocks firmly on the ground. Hold for at least 30 seconds, and then stretch the right side.