The details required to reference a book are available on the title page of a book and its reverse page (verso).
There are some points to keep in mind when using this information.
An eBook that includes all the same elements as the print version e.g. page numbers, edition, publication details, should be referenced as though it was a print book.
If the ebook is available on an edevice (Kindle, smartphones and tablets) the elements might not be the same as the print version. If this is the case you need to use the information you do have e.g. loc or %
(Adams, 1979, loc 876) or Adams (1979, loc 876)
Adams, D. (1979) The hitchhiker's guide to the galaxy. Available at: http://www.amazon.co.uk/kindle-ebooks (Downloaded: 28 August 2013).