I find these sorts of essays difficult. Not because I can't think of anything to say—gnomic pronouncements are plentiful in the writing world—but because I don't think it makes any difference. Good writers figure it out on their own. Good writers develop a style that works for them. They write, they fail, and they write again. The trick is prying apart the words, the sentences, the paragraphs, and seeing how it all works. Good writers intuitively know this. They certainly don't need me getting in the way.
So in honor of that self-immolating preamble, I give you the only useful advice I can muster: cultivate selective stubbornness. The writing life is filled with rejection and false starts, big risks and small payoffs. You've heard all this before. You know teachers will be disappointed, friends will disapprove, agents won't respond, publishers will scoff. Being selectively stubborn is a wonderful shield against these assaults. By "selective" I mean paying attention to the right folks—a good writer can tell who's a right folk within minutes—and completely ignoring the rest. It also means not lying to yourself. Hemingway called it having a "built-in bullshit detector." I can't improve on that.
Anyhow. I hope my advice proves frustrating. Why? Because the stubborn bastards won't care. They'll keep on writing. As they should. As you should. Get to it.