It takes a lot of time, practice, mistakes, and dust to get it right. I watched and assisted my uncle (a master) on about 3-4 rooms before I tried to tackle one on my own... a 3'x8' hallway. It took me about as long as it took him to do a 12x15 bedroom and didn't look nearly as good.
You can get a book or buy a video, but if money isn't a huge obstacle, you might be better off paying someone else to do it. Especially with the money you'll spend buying the tools and supplies to do it right in the first place. Depending on the size of the room/wall and the amount of things you have to tape and fill, of course. If it's one small wall this might be a great learning experience. =)