Once, on a visit to a Warli tribal area in India, an NGO volunteer informed me that the tribals, famed for their incredible line art, didn't follow any design principles, they just started drawing, following one line with another, one form with another. They are completely clueless about design rules, he said, with the superior twitch of one more clued-in.
I had to admit I was in the same boat, that I knew about as much regarding design, that I too followed one line after another, one form after another, one color with another, until harmony and balance were reached.
I've read up plenty on design principles since then and the sound ones are really all about good aesthetic sense and logic and creativity. It is helpful and certainly mind-broadening to know them, but, keeping topical considerations in mind, my actual design-making process is still fundamentally the same and is best illustrated by this conversation between Frank Sinatra and Luciano Pavarotti, as related by Vincent Falcone -
Sinatra: "How do you do that? How do you get that quality and strength of voice?"
Pavarotti: "I open my mouth."
And further on -
Sinatra: "Maestro, I'm having trouble ending a note. What should I do?"
Pavarotti: "Justa closa your mouth."
Keep things simple and uncluttered, that's the maxim.