Last year I recommended the ten professional books that I had found most valuable. I recently finished reading Contagious: Why Things Catch On and found it incredibly enlightening. The author, Jonah Berger, is a Wharton professor who is probably the leading expert on generating word of mouth.
Word of mouth is one of those black boxes that many growth or marketing professionals resignedly claim is a matter of luck. Berger, who has spoken to Google and Facebook among others, shows the fundamentals of creating a product that will generate word of mouth (the growth of which is not necessarily marketing, but rather integrated with building your game the right way). I will write more about Berger’s work in the future but you should put it at the top of your holiday reading list.