Generally it helps to be quite experienced before you teach, esp with something as deceptively simple as cycling. Since we mostly learn as children it seems trivial, but its probably as tricky a skiing.
Its important, for reasons of confidence , to learn to brake before you ride. Brakes will stop the bike, but not the rider, so riders need to brace against the bars. You can practice braking with a low saddle and no pedals.
Contrary to popular opinion, you dont turn bikes with the bars. You use balance to turn, and steering to regain balance. The natural path of a bike is an S curve, which experienced riders make so flat it looks like a straight line. Beginers should travel in an exagerated S curve, swooping in and out of cuves. Too many beginers try to cycle slowly, steering in the direction of travel, trying to stay upright by balancing. That is very difficult.
Begineers should wear helmet and gloves, long trousers and long sleeved jersy, mainly to prevent grazed skin. Practicing on a gentle grass slope is good. If they fall, the natural reaction is to break the fall with the palm of the hand. Bad idea. This will jolt your shoulder and may break a collar bone. A slow speed fall is best tackled by keeping the elbows and head tucked in, and relaxing into the fall so you impact with your shoulder. It really doesnt hurt.
Pick a smaller sized bike to learn on, with a womans /girls style frame, and if possible, single speed . Something cheap and simple. Its not the best kind of bike for riding, but makes learning simpler.
I was a sports instructor at college, and learnt that people dont respond well to verbal instruction, you need to prod and poke them to get the right position, and demostrate rather than lecture.