I contact first the author if he is willing to do a book review of another book (thats also exposure as he gets of course talked about, link back to his book etc.) and or interview with the author.
You have the author of an UPCOMING book review someone else's book, right?
How do you get the author of the UPCOMING book to agree to that? Is it just so they can get a blurb on YOUR site that says "John Doe is the author of the upcoming book, 'Blah, Blah, blah' by XYZ Publishers."?