The most important thing to bear in mind while stretching is that each person's body is unique. The challenge is to stay in touch with your own body, and make sure that you don't overdo it.
It is especially important that you give the highest authority to your own body's wisdom, since I am not an expert. I am just sharing, as a friend, these stretches that I have gathered from various yoga facilitators and physical therapists over the last few years.
In the gym they say, "no pain, no gain". In yoga they say "no pain, no pain!" Speaking from personal experience, if you push too hard, things can snap. So please be careful and use common sense, don't push too hard, and listen to your body.
~ Lie on your back; lift right leg so that foot points to ceiling; bend left knee out to the left. Place left foot on right thigh (bending right leg if you wish). Reach left hand through the angle of left leg and clasp hands behind right thigh; pull right thigh towards abdomen; hold. Reverse.
~ "Cradle the Baby": sitting with right leg straight out in front, bend left leg with left knee out to side. Place left foot in right elbow or hand, and left knee in left elbow. For more stretch, lift left leg higher and then pull it in closer. Reverse.
~ Gaumukhasana ("Cow's face position!"): Sit up on sitting bones with the help of a blanket. Cross right leg in front of you, with knee pointing towards the front, and right foot close to, but not under, left buttock. Cross left leg over right, so that eventually left knee will be over right and left foot will be next to right buttock. Gently lean forward if you need more stretch. (To stretch the chest at the same time: bend left arm behind back with elbow down. Bend right arm behind head with elbow up. Clasp hands if you can. If you cannot reach, use a cloth between your hands. Then bend forward with sitting bones still in contact with floor.) Reverse. Hold each side for at least 2-3 minutes. These are tough muscles.
~ "The Box": Sitting on sit-bones, cross right leg in front with knee pointing diagonally to the front/right. Cross left leg on top. Left outer foot is along the outside of right knee. Left knee would drop into right foot's arch if the hip were flexible. Reverse. (Each side 2-5 minutes.)
~ "Anton's Pigeon": Go into a lunge with right leg straight behind you and top of right foot and toes on the floor, and right knee off the floor. With sole of left foot flat on floor and not far in front of left hip, turn left foot and bent left knee out towards left. Look back over right shoulder then return to face front. Gently lower right knee, left hip, and torso towards floor until you find a good stretch. If you want more stretch, try turning left knee and foot fully 90° to the left. Use pillows or other supports under torso to relax into the stretch longer. Reverse to stretch right hip.
~ "Pigeon": Similar to Anton's pigeon with right leg extended behind you, and left knee bent out to left, but now with left knee, lower leg, outer ankle and foot lying along ground perpendicular to torso and straight right leg. Keep center of gravity over straight leg. Again, supporting torso with pillows may help relax into the stretch.
Hips and legs
~ Sit with both legs out in front. Use a blanket under the back edge of your buttocks to help you sit up on your sitting bones.
a) Let the in-breath help you pull your toes toward you; the out-breath helps you point your toes away from you. Then the same with the whole foot. Next, keeping in tune with the breath, circle the ankles: first together in each direction, then in opposite directions. Clasping hands under one knee, bend your knee and pull thigh in towards trunk with the in-breath; on the out-breath straighten your leg and point toe. Reverse.
b) Cross left foot up on right thigh, as close to the trunk as you comfortably can. Support left foot with right hand, and let left knee point out to your left. Use left arm to pull left leg towards you on in-breath; down towards floor - gently - on out-breath. Then other side.
c) Starting in same position as in (b) above, circle knee in each direction in tune with the breath. Reverse. (From the Bihar School of Yoga)
Backs of legs
~ Lie on your back with tailbone (coccyx) on the floor and sacrum off the floor slightly. Bend both knees slightly and rest soles of feet on floor. Lift left leg (bent is fine) and "point" the ball of the foot towards ceiling. Clasp hands (or wrap a cloth) over ball of foot and gently pull leg down towards trunk. Right leg can be straight if your back is strong. Reverse. Lifting both legs together is the next step.
~ Standing near a step or low table, put left foot up on the step-table. Lean belly towards thigh with back straight. Reach with your belly not with your shoulders. Reverse.