I agree with what most people have said about having a trainer to guide you, READ everything you can get your hands on, and spend lots of time with your horse...
The one thing I've read a lot in this post is people saying that you need tons of experience to train a horse - BUT you have to start somewhere. Every trainer with lots of experience trained their first horse at some point in time. And yes, it probably didn't go as well as planned but you learn from your mistakes and I doubt the horse will be useless or dangerous if you make a mistake now and again (which is unlikely if you are "supervised")... horses are forgiving creatures, if you make a mistake and correct yourself and try again you will most likely (eventually) see positive results.
I just don't ever like to see people discouraged from trying something new...you have to start somewhere.
This said, obviously having some one guide you is a must for your first time ... so good luck and have fun!
I train horse as a part time job...even though it seems like full time lol. But the best way to learn how to train horses is from the people around you. Accept criticsm. Theres always more then one way to do something so hear everyones opinion. I have never followed a book to train horses, I find that it only works on those calm horses that accept everything lol. Also just be creative. With groundwork sacking a horse out with everything possiable can get kinda fun. Me and my friend made a dummy to put on the horses, but you gotta be careful with that, he's got break away straps. NEVER tie something to your horse make sure it cane asily fall off if it needs to.
I train my own horses. Yes, I did teach myself how to train. Mostly by experience, books and magazines. I had some help from a local trainer, but his methods are a little too crazy for my liking.
Training is no easy job when you don't know exactly what to do and don't have someone who knows the exact situation you are in to help you. If you get stuck or lost you have to figure out how to do it on your own. There was a point when I believed I could train a young horse all by myself. However, I didn't know the begining of it. I had no idea what lateral flexion was or how to get the correct lead. The thing is You don't know how much you don't know until you know it. If I would have gotten a young horse at that time I would have not been capable of training it.
My advice: yes you can teach yourself and don't be scared of my story. I don't know how much you already know, but I would still recommend searching for all the information you can get. Books are great. I learned a lot from TV (RFD-TV especially). I need to be able to see how it is done in real life and not just in 2D in a book or magazine. However, I enjoy magazines because they have more specific and advanced information.
I train my own horses. It comes naturally to me. I always have except for when I first started riding. The first year I had some guidance. I didn't read books, but I just taught myself and watched some professionals a little. I trained a horse from 1 1/2 years old to go on to do quite well in a seven state competition. It isn't something to be taken to lightly though. Any horse, even the sweetest thing, can hurt you. I'm only 15 and I don't really know how I got to train my own horses, but oh well. Have a trainer help you right now. That's what I'd say.
I have trained every one of my horses and I love it. I am now beginning to make a career out of it. It is very hard work and you have to be willing to get hurt a few times because its going to happen sooner or later! I love training horses, but it takes patience and passion. It is such a great sense of accomplishment when the horse understands what you want to teach it.