I am breaking that rule right now. I really liked this paragraph from a longer post in which the language gets a little salty.
No matter what kind of writing you do—short stories, books, children’s lit, screenplays, stand-up bits, whatever—don’t ever approach it as though you’re trying to please an audience. Don’t ever write what you think people want. Don’t ever write about something you think is popular. Because invariably, it will suck. And it will suck hard.
Write to please one person and one person only: yourself.
Which is to say, write the kind of book that you love to read. Write the kind of script that you want to see on the screen.
That came from here and the few other posts I read were good also. Check it out. But be warned, salty.