Every successful piece of nonfiction should leave the reader with one provocative thought that he or she didn't have before. Not two thoughts, or five - just one. So decide what single point you want to leave in the reader's mind.
William ZinsserUltimately the product that any writer has to sell is not the subject being written about, but who he or she is.
William ZinsserTips can make someone a better writer but not necessarily a good writer. That's a larger package - a matter of character. Golfing is more than keeping the left arm straight. Every good golfer is a complex engine that runs on ability, ego, determination, discipline, patience, confidence, and other qualities that are self-taught. So it is with writers and all creative artists. If their values are solid their work is likely to be solid.
William Zinsser