Like most people here, I started teaching informally - assisting my instructor with classes and, eventually, covering some classes for him if he couldn't make it or was out of town or whatever.
The first time I taught "on my own," though, was a pretty harrowing experience.
I was 1000 miles from home for work. I visited a school and attended some of their classes. The head instructor at the school was simply incredible (and I later moved down there and spent a couple years training with him) and his senior students really seemed tight. One of the senior instructors at the school had a lame knee (had surgery on it a week after I left, in fact) and wasn't getting around very well. On Tues night, he asked me if I would cover his Thurs night class for him because he didn't think he'd even be able to walk.
At the time, I had no formal instructorship ranking in anything. I was a seasoned veteran of the martial arts with about 20 years of training under my belt but I was still a year from testing for my instructorship under my primary instructor. Now this man who I had just met had asked me to teach a class for him.
First, I called my instructor back home. Since I would be representing him (at least in spirit) abroad I figured I should get his OK. He said, and I will remember this until the day I die, "Blow 'em away." No pressure there, right?
I had no idea what skill level the instructor I was covering for really was - much less where any of his students were. All I knew for sure was that all the instructors in the school that I'd seen teaching ranged from good to really freakin' good.
I was nervous as a 80s prom queen near open flame (it's a hair spray joke in case you don't get the reference

). But I've always been pretty good at putting nerves aside at crunch time so when I stepped onto the floor I wasn't really all that nervous - the time for nervousness had been the two preceding days. I figured, "I'll do my best and it'll either be good enough or it won't."
I wound up having one of those days where I could do no wrong. I couldn't have screwed up a technique if I tried. Everything just clicked and flowed smooth as silk across marble tile. The head instructor of the school came and watched part of the class and, afterward, complimented me on my teaching.
That experience was a big one for me as a teacher. There were other experiences that tied into the epiphany I had but that was one of the big ones. The epiphany can be summed up thusly:
- I have (usually) been invited to teach so, apparently, someone figures I have something worth sharing.
- I am not teaching the material. I am teaching my perspective on the material. This one is huge! No one in the world - or, for that matter, in the history of the world - has ever had my perspective (on the material I'm teaching or on anything else, for that matter). Consequently, it doesn't matter who's watching. It might be the person who taught me the material or the founder or grandmaster of the system I'm teaching. It doesn't matter one iota because I'm teaching my perspective. I may not have any material to teach them but if they're open minded they can almost certainly learn something from my perspective on the material.
- What's the worst that can happen? I guess I could make a fool of myself but - see #1. I'll get up and do the best that I can and not worry about what anyone thinks. I know my stuff - I've spent (literally) more than ten thousand hours working on it. If I don't let my nerves rattle me then all anyone is going to see is that I do know my stuff.
Now, your "time in" might be less than mine. No shame there. If you've spent hundreds of hours training what you're teaching (which is about the bare minimum for anyone who has attained instructor rank in something) then you probably know more than most of the people in the room. And the people who know more will understand - we've been there, too
Since I had this epiphany (or, really, a series of "oh!" moments that led to a big epiphany), I have had no problem teaching/presenting in front of anyone or any size of crowd - and I've had some doozies. Whether it was teaching in front of the founder/grandmaster of the system I'm teaching or presenting a demo in front of (literally) tens of thousands of spectators in a huge arena in China (it was sheer madness - but in a good sorta way - at least in retrospect

) Or even just walking into a teaching situation where I don't know anyone else in the room or their ranks or anything.
For me, it always goes back to the fact that
no one in the world has had or ever will have my particular perspective on the material - and that perspective is what I'm actually sharing with people.
Mike