Huh? Teaching an adult? I dunno how to teach...but i guess, dun
scare the adult too soon, let him/her feel safe and comfortable,
e.g. bike shd not be too high/big frame, ask them to look in front,
and not down at their feet or the front wheel (and lose
balance).
I have a gf who was terrified out of riding, bec. the wrong bike
size (borrowed) was chosen for her. Now she absolutely will not try
it, even with smaller and safer bikes. 
