Definitely if you are going to start look for a trainer to walk you through it. I learned by watching a couple times, then trial and error with no one watching me. I got kicked once, I got too close to a very annoyed mare...(it ended well and I had learned my lesson though!) If you do it wrong it can be unsafe and hurt your relationship...
I am curious welshrider, what are you hoping to gain by trying join up?
Like I said, I am for it. Although it does not replace regular ground work it can work wonders done properly.
I also have never done it on a horse that was afraid of me, and would not use the approach I described at all with a horse that was. Depending on the level of fear join up may still work, but it would be handled entirely differently. Most of the horses I've used it on have not only not been fearful, but also lacked respect for humans.
Every horse is different and experience is what will tell you how to handle each one, in join up or otherwise. While you're still earning the experience a good trainer can tell you instead ;)