"Where do you get your ideas?" is still the question I get asked most as an author. The second-most-asked question is "How do you write a book?" The answer to both questions is simple: I don't know. But I can tell you how I do it.
Writing, like any art form, is whatever you can get away with. If you do it well enough, you can do anything. So forget all your English Comp 101 rules. Relax and let your own voice come through. Faulkner doesn't sound like Margaret Atwood, who doesn't sound like Cormac McCarthy, who doesn't sound like China Mieville.
Listen to your instincts and listen to the story. Most stories want to be told a certain way. You need to figure out what that is and write them that way. Past, present, or future tense. First, second, or third person. (You better have a damned good reason to write a story in second person or future tense). When I started Sandman Slim I tried every combination of tense and voice I could think of, but the book wouldn't budge. Finally, when I succumbed to first-person present tense, it took off like a bottle rocket out of a carnie's ass.
Feel free to break grammar rules, especially in dialog. Remember that copy editors might be accurate, but they aren't always right. When they want to change your prose to something that fits Strunk and White but doesn't flow on the page, feel free to argue.
"Everywhere I go I'm asked if I think the university stifles writers. My opinion is that they don't stifle enough of them." – Flannery O'Connor
Forget creative-writing classes. Study journalism. Learning to structure and write a simple declarative sentence is more important than oh-so-clever prose. When you learn to write clearly you can add all the frills and geegaws you want.
If you don't have time to write, look for it. Maybe do it in the morning before everyone gets up. Maybe do it at night while everyone is asleep. Back when I still had a straight job, I brought my laptop to work with me. I stayed an extra hour every day and wrote at my desk because I knew I'd be too tired when I got home.
Find what tools work for you. These days I use Scrivener to assemble my notes and to outline. I make a lot of notes by hand so I try to do them on the iPad with the WritePad app. It turns handwriting into a text file that you can download or sync with Dropbox. When I make notes on paper, I usually use a Sharpie on a legal pad. And I always have a pad with me — sometimes a small Moleskine Reporter notebook but more often a Little Black Book notebook. They're spiral bound so I can easily rip out the pages and put them in a pile to transcribe into Scrivener.
When you feel free to break all the writing rules you learned in school, you can find yourself in a void. What I mean is that when there are no rules anymore, you have nothing to bounce off of. No guides to help you rein in your writing when it gets too precious. After a 50-plus-year writing career, Elmore Leonard came up with his own prose commandments. They're simple and clear, and they make a lot of sense. I don't agree 100 percent with all of them, but that's fine. Learning what you don't want to do is just as important as learning what you do. Take a look at Leonard's rules and think about them. You'll probably find something that will help your work. If you do like them, there's a small-book version available.
Elmore Leonard's 10 Rules of Writing
1. Never open a book with weather.
2. Avoid prologues.
3. Never use a verb other than "said" to carry dialogue.
4. Never use an adverb to modify the verb "said"… he admonished gravely.
5. Keep your exclamation points under control. You are allowed no more than two or three per 100,000 words of prose.
6. Never use the words "suddenly" or "all hell broke loose."
7. Use regional dialect, patois, sparingly.
8. Avoid detailed descriptions of characters.
9. Don't go into great detail describing places and things.
10. Try to leave out the part that readers tend to skip.
"Write what you know" is the biggest lie an English teacher will ever tell you. What you know isn't what books are about. Books are about what you can imagine, from Tolkien's Hobbits to Fitzgerald's Gatsby to Chandler's Philip Marlowe. Trust your imagination, but don't get too pleased with yourself. Someone else probably thought of the idea first. And do your research, especially if you're writing science or historical fiction.
William Faulkner on Ernest Hemingway: "He has never been known to use a word that might send a reader to the dictionary."
Hemingway on Faulkner: "Poor Faulkner. Does he really think big emotions come from big words?"
One last thought: No matter how experienced you are, no matter how many stories or books you write, they're never going to be good enough. The story in your head is always better than the one that ends up on the page. That's just the way things are. Which brings me to the only writing rule worth a damn: work hard but give yourself a break. I guarantee you that Shakespeare thought Hamlet was just so-so.