First one from C.S. Lewis (courtesy of Advice to Writers, at http://www.advicetowriters.com/:
Even in literature and art, no man who bothers about originality will ever be original: whereas if you simply tell the truth (without caring twopence how often it has been told before) you will, nine times out of ten, become original without ever having noticed it.
I like that one. But I like this one even better:
Don’t worry about people stealing your ideas. If your ideas are any good, you’ll have to ram them down people’s throats.