Use less technical terms as possible. Explain every technical terms you have mentioned (eg. array, object, function, etc.) or don't use that term.
Explain why you should to this instead of that.
Teach with real-life examples & use cases, plain simple web server always win OOP principles.
Less startup time (Setting up Ruby vs PHP w/ LAMP)
Go slow, everyone has different paces.
Skip unnecessary details, don't teach everything, emphasize only important points.
Make it fun!
Hardware coding on Arduino
3D-Modelling & Printing with Sketchup & Slicer
Ruby with simple web server (Sinatra)