Welp, here goes - how to teach people stuff

I volunteered to give a couple of my co workers a basic "intro to knitting" lesson today over lunch and help establish a group hang out with crafters who nibble at lunch once a week. So I have some plans and some hopes and also some concerns!  

Have you ever taught someone something? were you super prepared about it beforehand or just relying on your own expertise to carry you thru?