Mostly a lot of experience. I have a mechanical engineering degree but basically grew up in a fab shop and started working on serious vehicle stuff (tubed out stock car, blazer, etc) in high school.
My dad's done some of everything so far, there's really not much he can't pick up quickly or has already done.
Beck's a ME also and had some fab experience before he came here and is picking up a lot more.
Jeff's actually a harley riding tatoo artist but something about being good with his hands and detail oriented makes him good with transfer cases and keeping up with small parts.
I'd recommend experience as a very good thing to pick up. Find a shop you can work in or at least do some involved projects yourself to practice and improve your own fab skills. You should also look at some kind of business or management education. That kind of knowledge can take you a long way.