Be yourself. What makes your voice unique is simply the fact that you're you, so be yourself completely and fearlessly in your writing. Get your personality on the page. Dive into your passions, sorrows, joys, idiosyncrasies, insights, your personal myths, monsters and miracles. This doesn't mean you need to write about yourself, you just need to write like yourself. Only you can be you and only you can write like you-that's your gift alone.
Jandy Nelson
See to your gusto. Ray Bradbury said, ". . . if I were asked to name the most important items in a writer's make-up, the things that shape his material and rush him along the road to where he wants to go, I could only warn him to look to his zest, see to his gusto." It's crucial to explore characters/events/times/places/ideas that fascinate, horrify, confuse, impassion, enflame, confound, delight you, things that see to your gusto.
Throw rocks at your characters. Someone smart once said: Not only do you have to chase your characters up trees but once they're up there, you need to throw rocks at them. Characters need to get into trouble. Do not protect them or care what readers will think of them. Conflict, whether internal or external, makes stories.
Writing is revising. As Anne Lamott advises in her wonderful book on writing Bird by Bird: Allow yourself to write a terrible first draft. Then you will revise, revise, and revise some more. But you need that first draft to begin the real work of writing a novel.
Curb toward joy. When I was in graduate school, I took a literature class for writers with Edmund White. One day in lecture he talked about how writers can get gloomy: always alone, tapping away at their keyboards for years, often with no support or feedback, and so to compensate for the potential dreariness that might seep into the work purely circumstantially writers might remember to curb toward joy. This idea hit me like lightning and has stayed with me since.
Kill your darlings. An oldie but goodie. Samuel Johnson wrote, "When you come across a passage you think is particularly fine, strike it out." Love this. Don't be writerly, be you.
Take your time and to thine own self be true. Don't rush and don't feel pressure to show or send your work out until it's ready. Do not think about the market. Write the story you must write and take the time needed to tell it the best way you possibly can.
Sit in the dark. Another YA writer I know plays the same song over and over again all day long while she writes. I write in a dark room with earplugs in and sound machine blasting like a loony. Find the way to work that works for you.
Remember writing is magic. If you write fiction you get to live so many lives in your one lifetime. This is brilliant sorcery-enjoy it!
Read every amazing book you can get your hands on.