Kurt Vonnegut's rules of writing:

Now lend me your ears. Here is Creative Writing 101:

1. Use the time of a total stranger in such a way that he or she will not feel the time is wasted.
2. Give the reader at least one character he or she can root for.
3. Every character should want something, even if it is only a glass of water.
4. Every sentence must do one of two things -- reveal character or advance the action.
5. Start as close to the end as possible.
6. Be a sadist. No matter how sweet and innocent your leading characters, make awful things happen to them -- in order that the reader may see what they are made of.
7. Write to please just one person. If you open a window and make love to the world, your story will get pneumonia.
8. Give your readers as much information as possible as soon as possible. To heck with suspense. Readers should have such complete understanding of what is going on, where and why, that they could finish the story themselves, should cockroaches eat the last few pages.

The greatest American short story writer of my generation was Flannery O'Connor. She broke practically every one of my rules but the first. Great writers tend to do that.

And then he goes on to add this:

I'm almost sure she [O'Connor] didn't break rule seven. The late American psychiatrist Dr. Edmund Bergler, who claimed to have treated more professional writers than any other shrink, said in his book The Writer and Psychoanalysis that most writers in his experience wrote to please one person they knew well, even if they didn't realized they were doing that. It wasn't a trick of the fiction trade. It was simply a natural human thing to do, whether or not it could make a story better.

Dr. Bergler said it commonly required psychoanalysis before his patients could know for whom they had been writing. But as soon as I finished his book, and then thought for only a couple of minutes, I knew it was my sister Allie I had been writing for. She is the person the stories in this book were written for. Anything I knew Allie wouldn't like I crossed out. Everything I knew she would get a kick out of I left in.

Allie is up in heaven now, with my first wife Jane and Sam Lawrence [who Vonnegut credits with saving his career by republishing his novels when he finally found an audience] and Flannery O'Connor and Dr. Bergler, but I still write to please her. Aliie was funny in real life. That gives me permission to be funny, too. Allie and I were very close.

- from the author's introduction to his short story collection, Bagombo Snuff Box.