I didn't want to mix this in with my post about the mistake of responding to reviews, because I wanted to avoid the implication that reviewers behaving badly brought it upon themselves. No reviewer should ever expect to be flamed, called names, sworn at, or harassed in the pursuit of telling people about books she's read, no matter that reviewer's approach. Just as people have different tastes in books, people have different approaches to reviewing. There's no right or wrong way.
When I write a review, these are the general standards I hold myself to:
Review the work, not the author.
I try not to make any personal comments about authors, guesses about his or her private life or sweeping statements about an author's entire body of work based on one book, or even a small sampling. I may refer to other works as a basis for comparison, but not to condemn everything an author has ever written. If I generalize that everything this person wrote sucks, I'm lying, because I don't give an author that many chances to waste my time.
What's it about?
If it's a well-known book or the synopsis is better than anything I could come up with, I won't bother with a plot summary. But often, I'll put at least a sentence or two about the basic plot.
I've gone back and forth on this point, and finally decided that I'm writing to people who haven't read the book yet. I'm always annoyed when major plot points are given away before I've read or seen something, so I don't put it out there in my reviews. If I must, I'll find a place clearly marked as, "Spoilers ahead! Keep out!" and talk spoilers there.
Try to find something nice to say.
If it's a published book, obviously some publisher somewhere saw something about it that was supposed to appeal to readers. The least I can do, even if I hated the book, is pass along what kept me reading (or listening) until the end. Maybe what I hated is something other readers like, and the one thing I liked is enough to make them want to read it. I'm not doing the book justice if I'm tearing it apart. If I couldn't even finish the book because of how little I liked it, I don't review it.
Be open about biases.
If I'm reviewing a romance novel, I have to be up-front about my aversion to the alpha male trope (seriously, it's why I don't usually read romance novels), because lots and lots and lots of readers enjoy that in a romance novel. If I adore a particular author, I mention that in the review, because it'll skew my review toward the positive. People need to know on what basis I'm judging a book.
Are there any standards to which you hold your book reviews? What are they?