I think this is generally true for instructing of all kinds --
First, make sure you actually want to teach. I'm a senior engineer where I work and "teach the junior people" is a job requirement. Which I happen to enjoy, so I had planned at one time to retire as a public school teacher. I'm a masochist, I know.
I learned mostly by teaching junior people within my department(s), doing seminars at conferences, things we call "technology transfer" where architects and lead designers teach others how the stuff we designed works, and so on. I've not had any education or teaching coursework, I just learned it on-the-job over the past 10 or so years. When I do electrical work, I often do lay-person "education" -- safety talks and the like.
My advice, and again I think this applies to just about all fields, is to get some experience "teaching" either by teaching underlings or outsiders. I've done "show-and-tell" for friends (including an ex of mine who was in college getting an associates in network something-or-other), conference presentations, courses for clients and so on. Get feedback on what you're doing right, and where you need improvement. Lather, rinse, repeat.
A lot of instructors outside of the university environment have experience in their field with no formal education-field background (meaning, no liberal arts education in "education"). The instructor at the technical school where I spoke (ITT Technical) had industry experience with LAN gear, and that's what he did for his day job. I was there talking about designing networking software and network security. Which brings me back to Brian's comment -- you might be able to gain experience teaching or assistant teaching at a local school or JATC.