- Never ever attack the author.
Not only will it provoke a counterattack, it is completely irrelevant to your purpose as a book blogger, which is to review the book. A writer's sexuality, hair colour or parentage will not affect how they write. It may influence what they write -- but you can choose what you read, no? - If your review is less than complimentary, do not go out of your way to send the review to the author.
Refrain from @ tagging the author in Twitter. Don't leave a link on their Goodreads profile. Give your marketing contact a heads-up when you send your review to them so they know not to tweet it to the world (if, you know, they're not the type to actually read your reviews). Or else you're just asking for a reaction. - Write reasonable reviews.
"OMG this book sucks. I can't believe I wasted my time reading, I can't believe the author spent a year writing it, I can't believe the publisher even published it at all."
No.
"It's difficult to find a redeeming quality in this novel. With a constantly indecisive protagonist, a two-dimensional love interest and pacing that wavers like the new Dyson fan, it falls to the worldbuilding to hold the story up... and the worldbuilding fails to deliver."
Better, yes?
May the book blogosphere live on, friends. <3