“Know the rules well, so you can break them effectively.”
(Also, if you believe QI, there's debate about whether a classification of 'fish' can even exist since it covers such a wide range of species as to be essentially meaningless. But I'm not an icthyologist.)
Followed by "Of course there are always the great exceptions. Genius is far rarer than people think, and genius has ways of its own."
The problem I have with online quotations, including those from goodreads, is that few people make an effort to verify the quotation. For example, one of the variations I know is listed at http://www.goodreads.com/quotes/558213-learn-the-rules-like-... ; it attributes "learn the rules like a pro, so you can break them like an artist" to Picasso. However, I can find no citation to Picasso actually saying that.
Quotation is one of the places where I've found it best to reference something like Bartlett's Familiar Quotations. I actually did check my dated paper copy before posting, but it doesn't have an entry for a quote like this under "rule" or "break". That's why I just said it was a maxim. ;)
BTW, Snopes, at http://www.snopes.com/inboxer/hoaxes/dalai.asp, says the Dalai Lama didn't say/write the above attributed line. Instead, it's a false attribution in an email chain going around in 2000, derived from an older email chain, derived in turn from "Life's Little Instruction Book" (1991) which said "Learn the rules then break some."