This post is a follow-up to "Nail Click," this time with information. I have long been fascinated by the wonderful, pure tone of master musicians like Julian Bream, Keola Beamer, or for that matter, Bela Fleck.
Here is a link to advice from classical guitarist and music professor Michael Chapdelaine on how to improve your tone. It expands on Darin's response and offers a practice technique. So far so good.