One piece of advice I found especially helpful (even as a nonfiction writer) is when Saunders describes how he came to find his "voice." I use quotation marks here because Saunders points out that we have many voices. What we need to do is find the voice that is most energetic, even if it's not the spare, Hemingwayesque one we originally thought was ours.
When Saunders first found his "voice" (I will persist with the quotation marks), the story that resulted was the best he'd ever written, he said, but it was no Chekhov or Tolstoy. He felt he had let the short story form down. "It was as if I’d sent the hunting dog that was my talent out across a meadow to fetch a magnificent pheasant and it had brought back, let’s say, the lower half of a Barbie doll.”
In a world in which writing is taken oh-so-seriously, Saunders is seriously refreshing.