The most blatant piece of advertising connected with a book is the blurb. With the traditional hardcover and paperback formats it is on the back of the jacket with sometimes the addition of a catchy one liner on the front. With the ebook and audiobook, where to put it is not so clear but to gain the most benefit it must be placed on the website and all flyers, posters etc. where information about the book is displayed.
The blurb should entice the reader into wanting to read the story. It should never give away the ending. It differs markedly in this respect from a summary sent to a prospective literary agent or publisher who should always be given more including the ending.
Great tips for writing blurbs can be found at http://www.prarts.com/news_view.aspx?articleid=15&LessonID=2
A good account of the history of blurb writing can be found at http://www.themillions.com/2012/02/i-greet-you-in-the-middle-of-a-great-career-a-brief-history-of-blurbs.html
Examples of what some consider to be the best blurbs can be viewed at http://www.rtbookreviews.com/content/writing-stars-vote-best-back-cover-blurb