I have shelves and shelves of an ever-growing collection of writing books, with no end in sight. Some I've read, most I haven't, but I think of them all as an investment and most of them have come in handy for the classes I'm teaching this fall.
Yet on the other hand, it's silly because out of all of these books that I own, I remember the best writing advice I've ever received. My freshman English teacher constantly reminded us to "Say the most in the least amount of words", always striving for brevity and clarity. Those words have always stuck with me, and I find myself saying the same thing to my students (for some, it hasn't sunken in yet). I have no patience for the old "Write what you know" philosophy, because if writers just stuck to that, we'd be out of ideas in a few minutes. Out of all of the tips I've received over the years, that short piece of advice has always stood out above the rest.
What's the best writing advice you've ever received?