The first thing that (randomly) comes to mind Ed, is that the writing should be engaging--embedded in a narrative that mirrors the fascination of the field in whatever form works best for the intended audience. And, when I think back to reading Martin Gardner's columns in Scientific American when I was a teenager, I first think of Dr. Matrix (http://en.wikipedia.org/wiki/Irving_Joshua_Matrix) and, since I was a mathematically inclined adolescent, his daughter Iva.
