Mrs. BD was discussing the elements of design with me as she has been working on yet another one of her design projects. We talk about rhythm, balance, repetition, unity, etc., but, above all, putting the specs first. Like a sonnet.
We thought that this wiki entry, Design elements and principles, offers a beautiful and succinct summary of the topic. Each section can lead to nifty conversation about almost anything.
Design principles can apply to anything that anybody wants to make beautiful: art, gardens, clothing, buildings, furniture, tools, music, etc. Come to think of it, even writing stories or making up a dance.
I know somebody whose career is industrial design. Give him the specs and he will design a work of functional art. With talent, function can be made beautiful.
Consider the humble sinuous scythe. One of my grampas, the industrialist, was a pro with a scythe on the farm. In Yankeeland, pronounced "sigh." Sad to admit, I have always been lazy and partial to power machinery but a good man with a scythe can do faster and better with the added benefit of keeping in shape.