How does one practice a stage hypnotist show?

Better have a lot of friends.

Practice on friends, practive on imaginary people, practive hypnotizing one person at a time. Script your show, memorize it and perform it. Once you know the basics of hypnosis and can hypnotize one person, hypnotizing a group is easy.
No real way to practive a show, just gotta understand hypnosis, script it out and be narcissistic enough to pull it off the first time. I remember how amazed I was after the induction at my first show that everyone was out!

Ok, so perhaps it would be best to start off doing clinical hypnosis on a one-on-one basis and get good at hypnotizing one person... than move out on the stage?

To practice, even if you are never going to do clionical hypnosis, you will need to know how to hypnotize one person first. It is just easier to find one person to practive with. learn hypnosis in general, then take it to the stage.

Ok, I understand. Makes sense. Thank you.

Take Clinical training and get experience. The NGH has certified instructors, CI's (very complete clinical training) like me and a wide variety of other people and numerous organizations, and get used to working with hypnotized people, and then after experience, take stage show training with a Master teacher, who is not only a great teacher and cares about your success. Stage shows look easy if the Hypnotist knows what they are doing, but there really is a lot to know and master, working live in front of an audience, and quick thinking and thinking on your feet are also essentials.

Go into hypnosis yourself deep enough so that hallucinations can occur and practice from there. Just hallucinate out the whole ordeal.

I can imagine how hard that would be tho.