Author Kay Thomas pointed me to this enlightening and honest blog from the author of a Top 20 NY Times bestseller. This is the author's 18th book, which is an incredible achievement in itself. The entire posting needs to be read, but here is her opening statement, followed by the url.
"A few years ago I made a promise to my writer friends that if I ever had a novel hit the top twenty of the New York Times mass market bestseller list that I would share all the information I was given about the book so writers could really see what it takes to get there. Today I’m going to keep that promise and give you the stats on my sixth Darkyn novel, Twilight Fall."
http://www.genreality.net/the-reality-of-a-times-bestseller