When surfing Amazon.com, I see rotten reviews all the time. I don't mean reviews that convey a negative impression of the book or movie or whatever. I mean reviews that contain no useful information at all. So you don't want to write stinky reviews? Read on...
First Things First--Review the Right Book Yes, believe it or not, lots of people review the wrong book. When in doubt, check the author's name and/or the ASIN number. There may be several books out there with the same name. And if you review Eileen Kernaghan's The Snow Queen in the space provided for Joan Vinge's The Snow Queen, or vice versa, you haven't helped the people looking for info on either book.
Make sure you've READ the book. Or at least given it a good attempt. There are books I haven't been able to finish, but I'd never review a book I hadn't even looked at. When you write a review about a book you haven't read, it shows. For example, if you've read How to Turn Your Ex-Boyfriend into a Toad: And Other Spells for Love, Wealth, Beauty, and Revenge, you know that the title is metaphorical. People who haven't read the book write things such as: "You can't turn people into toads! It's wrong! Haven't you ever heard of karma? This is an evil book!" And people who have read the book think the others are twits. Don't be a twit.
Be intelligible Try to spell intelligibly and use punctuation. And don't write your review in all caps or all lowercase. It gives people a headache.
Say something!!! Most importantly, say something! Don't just say that this is the best book ever, or the worst book ever. Elaborate. Tell us why you liked or didn't like it.
Everything is Not Five Stars! 'Nuff said. If you rate everything five stars, then when you read something you really like, you have to resort to hyperbole and proclaim that it deserves ten stars, or ten thousand, etc. Yes, I've done this from time to time. I'm not perfect either. But I rate most things I read either three or four stars. It makes my five-star ratings a little more meaningful.
Do Unto Others I'm talking about those buttons where you vote whether a review is helpful or not. Be nice. Don't vote a perfectly coherent, intelligently written review unhelpful just because it disagrees with your own opinion. I've been insulted in others' reviews because I panned their favorite book, or even (oh! the horrors!) rated it only four stars. Refer to above comment. Everything is not five stars. And everyone is not going to like the same books as you do.
I find that a well-written negative review is very useful when shopping for books or other stuff. A few years ago, I read a scathing review of the movie Sliding Doors. But the review made me interested in the movie. I saw it, and loved it. If that review had been on Amazon rather than in the newspaper, I would have rated it helpful. It helped me decide whether to watch the movie. There are only a few reasons I rate a review unhelpful--if it is for the wrong book, if the writer clearly hasn't read the book, or if the writer makes bigoted slurs. I rate lots of reviews helpful, and still more I just don't rate at all. No need to be mean just because I disagree with someone.
After all, you want those "helpful" votes, too, don't you?