Hi ya,
Had my tongue pierced about 10 years ago now. I did alot of research before I had it done, as I had previously had my belly button done, but my body rejected it.
I had to make an appointment to go in and let the woman see my tongue before I had it done, (as you have major veins running under your tongue), also on some people, the flap of skin connecting the tongue to jaw is too far forward on some people to have it done, as it would just be rubbing and too uncomfortable.
The whole thing was throughly explained to me prior to having it done. My tongue wasn't clamped, although I did have to rinse my mouth with mouthwash prior to it, and sitting there with your tongue out and someone coming at it, with what I can only describe as similar to a metal kebab skewer, was rather un-nerving so I shut my eyes. I cant say it didn't hurt, but it was fleeting like an injection, and my tongue hardly bled at all, only like a trip to the dentist when they clean your teeth.
The biggest pain in the bum I had was with the beginner bar, my tongue didn't swell at all and I had difficulty eating, you are told to wait 5-10 days but I went back and got a smaller bar put in after 3 days.
I'm not a fast healer so I can take my bar out with no problems, although so people I know have taken them out and within 10 minutes theirs has started to heal. (This you can only know yourself). I don't like taking it out, because its just like I've always had it now, and feels really weird without it.
I'd say if you really want it doing, do your research so your confident with the person who is going to do it, always check their reputation, and if your happy with what you hear, close your eyes and go for it.