My ratings in reviews can vary from five stars to even zero stars.
The method that I use, though, changes depending on the book, so I don't always rate stuff with the same criteria.
Generally, what I rate about a book is the depth and structure of the characters, the writing and the storyline.
I try not to be one of those people who give low ratings only because they don't like a character. Now that is downright stupid, if you ask me. Like, if for example they don't like the male character or even the main character, then they're like "oh, this book sucks." But there's not only characters in books. There's so many things you gotta pay attention to when reviewing a book. And it's hard, so I don't pretend to be good at it or anything. In fact, my reviews tend to be more on the funny side so they're not really serious. Still, if you're going to review a book seriously you should at least try to cover all points.
Anyway. Everyone has their own method, and this is mine.
First of all, it depends on the genre. There are some books I gave 5 stars to, even if in the end they were pretty silly as storylines go. I rated them that way because the characters were built well, because the storyline was nice and funny and because the writing was pretty good all in all.
And then there's books like To Kill A Mockingbird, which is one of my favorites, to which I only gave four stars. Kind of confusing, huh? The thing is, an author has to decide what he/she's going to ventur on. It's like choosing which category in a competition you're going to participate to.
There are some books that are listed in the kids category, so even if they're not amazing they are pretty good as kids competitions go, so they get the max grade.
And then there's books who try the adult category, and maybe they don't get first. They're still great, but since the category was more difficult they didn't get the highest score.
It's kind of hard to explain, and maybe it's stupid to think like this, but that's the way I see it. If you want to try something hard, you have to be ready because people look for perks with much more attention.
And then there's the hook-up. Sometimes books are really great, but I'm just not into it so they don't hook me up. I try to be careful with my reviews with those ones, and take the blame in case I realize it's actually me who wasn't into it, and not the book that was bad.
Other times, though, books really aren't that great. Sometimes a book is just fine, but it doesn't hook you at all. You just read page after page with no actual desire of going on, if not for the sake of finishing the book.
So it's important for a book to interest people, and keep them interested throughout the whole story.
Sometimes, though, I'll be like "whatever", and give a book a high or a low rating because I feel like it. It generally happens with high ratings, though. For example, I finish reading a book and I KNOW there were a lot of incongruities in the storyline and there was something wrong here and some imperfection there, but since I'm in a good mood and I feel like giving a high rating and I liked it nonetheless, I give a high rating anyway.
I call them the moodings. As in, mood ratings.
What I meant by giving zero stars follows. Some people give zero stars to books they didn't like AT ALL. They think they were so ugly that they couldn't even give zero stars. While I kind of see where they're coming from, I've never actally given zero stars because of that. When I do give them, though, it's usually because I don't know how many to give the book, and I know that if I tried to decide my head would explode, so I just don't.
I guess that's pretty much all the basic rules of my reviewing. My ratings are really personal so sometimes they don't match with other people's, but mostly I try to stick with the impartial rules and try to give a rating that will really help people understand whether they'd like the book or not.