"How to Teach Someone to Use a Computer" — humane advice for techies from Phil Agre.
Be aware of how abstract your language is. "Get into the editor" is abstract and "press this key" is concrete. Don't say anything unless you intend for them to understand it. Keep adjusting your language downward towards concrete units until they start to get it, then slowly adjust back up towards greater abstraction so long as they're following you. When formulating a take-home lesson ("when it does this and that, you should try such-and-such"), check once again that you're using language of the right degree of abstraction for this user right now.
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