An irritated sciatic nerve can cause extreme pain in the back and legs. Most people experience this at some point in their lives, some more than others.
1. Standing piriformis stretch
Stand up and place one foot over your other knee. Lower your hips as if you’re going to sit on a chair. Hold this for a while until you feel your muscles stretching. Repeat with the other side afterwards.
Watch the exercise demonstration here.
2. Lying piriformis stretch
This is the same process as the first exercise, except you do this exercise lying down. Press the leg where your foot is on the ground towards your chest, while the other leg stretches out.

3. Hip stretch
Lie flat on your back. Bend your right knee so that it points towards the ceiling. Then twist your knee in the opposite direction (left) so that it is above the other knee. Make sure your upper body is facing directly towards the ceiling.
Watch how to do it here.
4. Frog stretch
Take a mat to lie comfortably. Sit on your knees. Stretch one leg behind you and bend your lower body forwards. You will feel this stretch, and that means it is helping. Repeat several times so the pain decreases each time.

5. Cross stretch exercise
Sit on the floor and stretch your legs as wide apart as possible. Lean forward if you can, until you feel the stretch. Hold this position.

6. Hip lift
This is an easy exercise. Balance on your hands and knees on a mat, and lift one leg up behind you so your heel points towards the ceiling. Lower and repeat. Do this about 5 times and alternate legs.
Watch the exercise here.
7. Sitting stretch exercise
Take a chair and sit up straight. Lift one leg up and place it in a way that your heel rests against your knee. Lean forward afterwards to feel the stretch in your buttocks and thighs.

Whether these stretching exercises will actually help depends on how often you perform them and how severe the pain is, but they helped me at least. Please share to pass on these tips to your friends.