Though this pose is often used as one preceding the scorpion, it is a complete pose in itself. I myself find that it is far more relaxing and satisfying pose than scorpion. In this pose you can safely stay for a minute or more, unlike with the scorpion where, if you are feeling stiff, or if the food was still in your stomach (late dinner or not a four-hour gap between meals), or a late night, or disturbed emotionally you can not be up for too long... Scorpion is exhilarating. Pincha mayurasana is all things at once -- exhilarating, satisfying, soothing. I am trying to work into the second stage of this pose, where instead of the lower arms, u are just resting on the elbows, cupping your jaw:) Sayanasana! . That one, though obviously one of the toughest poses, is called the sayanasana/ REPOSE pose:) They had a sense of humour, our yogis:) Or they were laughing at people who could not find repose in a difficult place.... the latter is more like it...!!!
In this, unlike with the scorpion, where you can bring palms together sometimes, the hands must be shoulder width apart. This gives it the balance more easily. You lift up from the shoulders, tighten the hips and legs and stay up against a wonderful drag. It is really one of the satisfyingly difficult poses there is. On a bad day I prefer staying in it longer to center myself ... It is that sort of a pose, almost like a standing balance.
If you are working on the scorpion, once you master it, you may want to work on pincha mayurasana as a separate pose because it deserves that sort of attention. It adds something to your personality -- opposites that are not at war with each other -- exhilaration that is soothing:)
Some of my students get this -- Amitabh (who the rains have claimed and he has disappeared under its lethargic pall:) used to move into this, before the scorpion. Sonia is training to stay longer in it. Mayank used to do this before leg-drop in scorpion. Mostly, it is for those who are unafraid of tipping over!!
What you need for this pose: Strength from shoulders, upper back. Neck and lower back flexibility (like the cobra, after a while this is where the pose hits you); hip strength (utimately, it is the hips that hold you aloft against gravitational drag).