There's a few issues with hypnosis. One, you have to trust the hypnotist with your life. If you don't, you will fight it and find your body jerking suddenly like you're trying to keep from falling asleep. It really doesn't help with things if your eyes are bolting open every time you convulse a little. If you don't trust the person you're willingly letting screw with your head, well, you'd have to be under the influence of something or just plain dense to let yourself go under.
Second, the hypnotist has to get all the little things right. The "subject" has to be comfortable, relaxed, at peace with the world (but preferably sober). There can't be any distractions, no traffic, ringing phones, barking dogs, all that fun stuff. Pull the shades, draw the curtains, unplug the phone, cover up all the light sources (like that flasing 12:00 on your VCR), have them lie down on the couch, and stare at a lit candle. This is the sort of thing that should be done by the person doing the talking. The subject is supposed to just chill the fuck out and not think about -anything-. Not a thing.
Then, the hypnotist has to actually have some sort of grasp on how to put someone under. Having a skeletonized script commited to memory so you can adapt as needed won't do much if you sound like Gilbert Gottfried or Sandra Bernhardt. Soft, soothing tone of voice. No coughing or sneezing. Quiet, repetative, peaceful. Best to practice on yourself (works wonders on a plane, just put yourself under and you're out like a light). You can find books in stores and howto's online. Just stick with the simple things like chicken clucking until you know what you're doing. And always be obscenely careful with triggers, mmmkay?