Here’s a link to a site with quotes by famous authors for writers. You can get there from here.

This is one I really love:

“Keep away from people who try to belittle your ambitions. Small people always do that, but the really great make you feel that you, too, can become great.”
Mark Twain

I like this one, too:

“If you would be a writer, first be a reader. Only through the assimilation of ideas, thoughts and philosophies can one begin to focus his own ideas, thoughts and philosophies.”
Allan W. Eckert