Some personal favorites (and why):
Whenever you write, whatever you write, never make the mistake of assuming the audience is any less intelligent than you are. (Rod Serling) - So sayeth the master storyteller. Good enough for me. And besides, who wouldn't rather write for an intelligent audience?
It’s none of their business that you have to learn to write. Let them think you were born that way. (Ernest Hemingway) - It's the same for actors and painters. They study for years to learn and perfect their craft. Why should writers be any different?
Make movies that make people laugh, cry, or keep them on the edge of their seats. (Carl Laemmle, founder of Universal Studios) - Something to keep in mind. We're not just writing to amuse ourselves, we've got an audience to entertain. Do not bore them. Keep them emotionally enmeshed in the story and with the characters.
Writing is easy. You just sit down at the typewriter and open a vein. (Red Smith) - An old chestnut that may sound melodramatic, but it's true. In a way writing is easy, because we love it, but there's also a lot of hard work involved.
If my books had been any worse I should not have been invited to Hollywood and if they had been any better I should not have come. (Raymond Chandler) - I think Chandler had a love/hate relationship with Hollywood, as he also said: Hollywood is wonderful. Anyone who doesn't think so is either crazy or sober. Either that or he was being totally sarcastic with that last one and I choose to be blind to it because I love this town and it's such a cool quote.