A friend asked if I had any advice on writing for her students. This was my very overdue response:
Write always. Carry a pen and a notebook around you. My workspace is full of sticky notes and napkins and scraps of paper that I've written ideas on. It's absolutely vital that you're ready to write these flashes of brilliance down when they come to you.
WRITE DOWN EVERYTHING.
Never, ever, absolutely ever, never compare your writing to anyone else's. You are not in the business of the being a J.K. Rowling or a Stephen King or a Stefanie Meyer. That's their job. Your job is to do YOUR kind of writing.
READ EVERYTHING. Absolutely inhale books. To create good muscles, you have to exercise lots. To create good books, you have to read lots.
Do it. I became a professional writer because I was tired of writing stuff at home in my room for free. I found an ad online and starting writing for them, and then starting approaching clients, and then clients came to me, and then I started writing for a magazine, and a newspaper, yadda, yadda yadda. No one is going to break into your room and read your amazing novellas. You have to stick your hand out in the universe if you want someone to read your writing.
To be a writer, all you have to do is write. to be an AUTHOR, someone needs to read your work. So, put it everywhere. Put your work on Facebook. Put it on your blog. Put it on the bathroom stall. Put it on the sidewalk in front of your friend's house.
NEVER throw away or delete your writing. That story idea may fit into another one ten years later. That snappy bit of dialogue that had no home in 4th grade will be perfect for that bit you write in college. Past writings, no matter how horrible you think they are, are fantastic footprints to show you how far you've come. I was reading a book that I had written and published two years ago. I mean, come on, that's the pinnacle of writing, right? And all I could think was "ick, did I really write that AND submit it?" and at the same time, you can look at something you wrote a decade ago and think "dang, that is GOOD." Never ever get rid of your old writing. Stick it in a folder in the back of your closet if you can't stand to look at it, but don't get rid of it.
This is a tough one: be willing to destroy your work. This doesn't mean burn all your old, horrible writings. This means that you need to be ready to delete that description of the old car, or admit that your favorite side character really doesn't have a place in this scene, or this story. The ink that flows from your fingertips is not always gold. Some stuff doesn't have a place in your current project and shouldn't be there. (that doesn't mean it won't be super handy when you're 45)
Realize that writing can be a pastime, a job, or a hobby. You don't have to be a best-seller unless you want to be. Pick the level of involvement you want, and don't feel pressured to be more or less than that. Regardless, realize that you are developing an incredible skill that will serve you well. You will write papers in school. You will write letters to future employers who you are trying to convince to pay you lots of money and give you dental insurance. Being able to write well--especially in the age of near-illiteracy that the Internet breeds--makes you a gladiator among barbarians.
Writing words means you're communicating. Literally, you're taking an intangible idea from inside your head and with a few scribbles you are installing that idea in another person's brain.
THAT. IS. INCREDIBLE.