Lay flat on fairly even ground/floor, preferably on soft and thin cotton bed mat. Should not practice on a small single cot or double sized cot to avoid any situation where there can be a risk of falling down from the cot to the ground of lower elevation bringing probable injury.
Soft mat is to be used to avoid pressure to the shoulder, head and neck regions.
No separate folds of rags or cotton sheet is to be used only for the shoulder, head and neck region. This makes the elevation higher, uneasy and strain the shoulder, neck and head with undue pressure.
Shoulder Stand Pose (Sarvangasana) is one of the most important yoga poses or asanas, particularly for the young people. Full-scale shoulder stand can pose problems for the age category beyond thirty or so.
For them having problems in neck and shoulder regions should avoid this one and go for Half Shoulder Stand Pose(Ardha- Sarvangasana). You can take the help of the Wall or somebody else if you have problem practicing as a beginner.
REMINDER :: Practice Fish Pose ( Matsyasana ) and Plough Pose ( Halasana ) after Shoulder Stand definitely. Practice of Fish Pose is mandatory after Shoulder Stand Pose, in case you omit Plough Pose. Practice Shoulder Stand four times of thirty seconds each with Corpse Pose of thirty seconds after each practice of shoulder stand (of thirty seconds ).
ALERT:: It must be followed by Fish Pose.
Fish pose is a very important backend. But instead of Bow Pose, follow Fish Pose after Shoulder Stand!