Things like fractures in the spine, herniated discs, spinal stenosis, and other physical problems may rule out autofellatio for some men.
There's really not much to it.
There are many approaches and methods of performing autofellatio.
Men are not alone in this interesting form of sexual stimulation.
Some use a wall for support and leverage.
Some men get extra leverage by pulling up with their hands on their body.
Men who are interested in speeding up the process of autofellatio are encouraged to read the book.
In women this is known as autocunnilingus.