The shoulder stand sex position requires a firm but padded surface to ensure comfort and protect the back and neck. (Sex furniture, like the Liberator Equus Wave, is made for this, but semi-firm beds may work too!) This is not a sex position for long-term play (it's too hard for most!) but it's a very fun and sexy add-on.
The partner performing the shoulder stand should take care not to twist their neck in this position. People with neck problems should avoid this position. To protect the delicate tissues of the neck, you should consider keeping the receiving partner's shoulders on the surface to bear the brunt of the weight.
This position works best for cunnilingus, but it can also be used for rimming with a bit of creativity.