Sarva = All/Entire, Anga = Limbs/Parts of the Body , Asana = Pose or Posture

‘Sarv’ means all, ‘anga’ means part of a body, and ‘asana’ is pose/posture. The word sarvanga implies that this pose, when practiced regularly, can bring benefits to your entire body. It particularly activates the thyroid and parathyroid gland. This asana is referred to as ‘Mother of all asanas’.

1. Lie back onto the floor, arms beside your body, with your palms facing down.
2. Inhale and raise your legs to a 90 degree angle.
3. Press the arms firmly on the floor and lift your back and lower your legs overhead behind you, until they are parallel to the floor.
4. Now, bring your elbows closer to the body and straighten up your legs. Your weight should be supported on your shoulders and upper arms and not on your head and neck.
5. If you want to make any adjustments in the neck, shoulder or hip, bend your knees towards your forehead, gently adjust, and bring the hands down to the middle back so the legs will be straightened.
6. Keep the toes pointed towards the ceiling. The chest may make a soft contact with the chin. 
7. Begin to hold the pose for 30 seconds and extend upto three minutes. Remember to do normal breathing while holding. Keep your eyes closed and concentrate your breath at the throat.
8. To come out of the pose, lower both the legs down overhead until they are parallel to the floor. Keep the palms on the floor and relax the lower back to the floor. Try to keep the legs straight and avoid lifting the head off the floor.  Finally exhale lower the legs to the floor without bending the knees.
9. In viparita karani, your chest and chin are apart and hips are lower, In sarvangasana your hips go all the way forward and  chest closer to the chin.

Tips :

If you are unable to lift the bottom off the floor with the legs straight, you can try a couple of simple variations to lift the body up into the pose.

Practice with Spinal rock

If you  are not able to lift your legs, you can do with a spinal rock stage 1  few rounds of practice and while you are rolling back just try supporting your back with the hands  and make sure elbows are closer to the body and lift your hip up, once you get your balance on your hip,  gradually straighten your legs

Practice with Viparita Karani

Practice viparita karani for few week before you try sarvangasana

Practice with Wall

1. Sit sideways, legs extending straight in the space between your support and wall. 
2. With exhalation, turn your legs up onto the wall and rest your shoulders and head on the floor. Adjust your back on the ground (forward and backward) so the hip comes directly towards the wall under the raised legs
3. And bend the knees, push the feet firmly against the wall and lift the hip up and bring the elbows closer to the body and support your mid or lower back. Keep the neck and shoulders relaxed
4. Close your eyes and breathe deeply for 30 sec to 1 min and relax.
5. After a few weeks of practice, you may attempt to lift one leg at a time off the wall.
6. When you feel comfortable, you may lift both the legs away from the wall and assume the sarvangasana and hold for a few seconds to a min.
7. If you feel you are losing the balance, again keep your legs on the wall.
8. When you relax the pose, reverse the steps, bend your knee one at a time, feet back to the wall, relax the hands, relax your upper back, mid back and tailbone/hip slowly. And keep your legs on the wall.
9. To exit the posture, gently bend your knees and push your body away from the wall. roll the body to the side and lie in the fetal position before pressing yourself up to a seated position.
10. After practicing with the wall support for a few times, if you feel you are ready, you can practice the asana without the support of the wall

Benefits

1. Sarvangasana involves raising the entire body up with the support of your shoulders and hands. It therefore reverses the blood flow.
2. It also increases blood flow to the lungs and can aid in respiratory issues.
3. It helps stimulate, prostate glands and thyroid.
4. It improves the flexibility of the spinal cord and has a positive effect on our nerves.
5. As the blood rushes backwards it benefits people with low blood pressure.
6. It helps improve the blood flow to the brain.
7. It activates the throat chakra.
8. It helps to regularize periods.
9. Improve function of the reproductive organ in both men and women.
10. It controls the blood sugar level and corrects the improper functioning of the pancreas.
11. Those suffering from sleep disorders promote deep restful sleep.