Advice if you're a young writer

I'm not the world's greatest writing teacher, but there's a few things I know. I actually never heard Francine Prose weigh in on whether it was a good idea to be writing what you know as the old saw goes. Edward Gibbon knew a lot about the decline and fall of the Roman Empire, but only because he spent all of his time studying it; he didn't know it first hand. His book appears on the list because there is no exclusion of the writers are not fiction writers. Her book is not aimed at fiction writers- as Gardner's were- but at any writers who want to learn from those who write beautifully. Show don't tell is another old saw. When Prose writes about an Alice Munro story, she shows that following the maxim would have made the story much worse. Clearly, she doesn't believe in its universality.