Trying to sound like Ernest Hemingway? Well,
that's not a bad place to start. Eventually, you'll
find your own voice. Image in the public domain.
And it doesn't even matter what they read. Comic books? Fine. Romance? Excellent. Manga? Go for it. Science fiction? Definitely. "Great literature"? (Whatever that is...) Sure! Read from whatever genre and in whatever format you like. Simply reading things written by people who know how to write will help you become a better writer.
And on the writerly side of things... I just tell them to write. Don't worry (yet) about whether what you're writing is any good. It'll get there. Sure, at first, 90% of what you're writing will be garbage. So what? Learn to tell the difference, and then use the remaining 10% to move on. Eventually, much of what you write will be strong, solid stuff. Just keep writing. If you don't quite know where to start, do what I do: start in the middle. Or at the end. It'll work itself out. That middle piece you write will suggest what the beginning should be like. That ending you wrote will help you fill in the middle.
Yes, at first, much of what you write will be crap, and derivative crap at that; you will probably try to sound like a favorite author. (At some point, we all tried to sound like Hemingway, right?) But that's OK. For now, go ahead; sound like a bad imitation of Hemingway—or Stephen King, or whomever. There are worse things to sound like. You'll eventually find your authentic voice.
The key here, of course, is that the student has to want to become a better writer. He or she has to care about the writing, has to want the communication to be effective. (And as an excellent writer by the name of William Van Winkle recently noted on my Facebook page, much of that effectiveness boils down to clarity, to a lack of ambiguity. I was lucky enough to work with Van Winkle during my days as a magazine editor. Check out some of his writing here. You'll be glad you did.)
So there's only one important thing that I really have to teach my students: I have to teach them to care. If they actually come to care about their writing, to think that clear, effective writing actually matters, then I've done my job. The rest comes naturally as an answer to the question: OK, so what do I have to know in order to do that? How can I achieve this clarity of which you speak?
Reading becomes a habit, and writers tend to be voracious readers. (In fact, reading—and being so enthralled and impressed by what we read—may have been what made us want to become writers in the first place. Holy crap! That was awesome! I want to do that!!, we thought in the 5th or 7th or 12th grades.)
My reading, for instance, is varied and constant. I'm always reading something (or several somethings), and I read everything from sci-fi to medical thrillers, from police procedurals to biographies, and from history to technical manuals. Right now I'm reading a biography of Ronald Reagan (personal political note: never in my life did I think that I would miss Ronald Reagan, but there you go....), a book about the making of The Princess Bride ("My name is Inigo Montoya. You killed my father. Prepare to die..."), a book about the risks of using drones in warfare, and Walter Isaacson's book, The Innovators, about the technologists who created the digital revolution. (I also just finished The Progeny, a thriller by my friend, Tosca Lee. And of course, there were the dozens of books that I read while researching Leveling the Playing Field.)
Reading is one of the things that makes fledgling writers into accomplished ones, and good writers into great ones. (I'm still working on "accomplished," and I dream—as do we all—of being "great.")