Robert A. Heinlein (1907-1988) was a American science fiction writer famous for such stories as “Stranger in a Strange Land”, “Starship Troopers” and “The Moon is a Harsh Mistress”. He had five rules for writing success:

Rule 1: You Must Write
Rule 2: Finish What Your Start
Rule 3: You Must Refrain From Rewriting, Except to Editorial Order
Rule 4: You Must Put Your Story on the Market
Rule 5: You Must Keep it on the Market until it has Sold

What may strike people as odd is that he doesn’t discuss things like plot, character development or grammar. Heinlein advice is really about staying focussed. Another sci-fi writer, Robert J. Sawyer, looks at these rules in more detail here: http://www.sfwriter.com/ow05.htm

(Source for the quotes: http://www.goodreads.com/quotes/421667-heinlein-s-rules-for-writers-rule-one-you-must-write-rule)