Before I start reading a new book, I only want to know two things about it: its basic plot and its average Goodreads score - a book that has an average score of 1 star doesn't exactly sound promising. What I don't want to know is the specifics* of why a person did or did not like a book, which is why I tend to only read a review of a book until after I finished reading it.
I am particularly averse to reading the lengthy (and frankly, long-winded) reviews you see in broadsheet newspapers and supplements. I've never understood the appeal of reading someone else's in-depth interpretation of a book when I could be coming up with my own interpretation by reading the book myself. For the same reason, I don't read introductions to well-known books - particularly as they often contain spoilers. I know that there are some people out there who prefer to read these types of reviews rather than read the book itself, but that seems a pretty pointless exercise to me. If they can't be bothered to read the book, why go to the trouble of reading a review of it? (If it's so that they can pretend that they've read the book, that's really quite pathetic)
That said, I do read reviews (but on Goodreads or blogs rather than in newspapers) when I am not sure whether or not I want to continue reading a book. Sometimes, a book really only gets going after the first few chapters; therefore, when struggling to get into a book, I read a review of the said book to see if it will get better if I persist with it.
Reviews in this context can also help you to know when you definitely don't want to keep reading. Recently, I was reading a book that I wasn't finding as compelling as I thought I would. Given that it had an average 4.76-star rating on Goodreads, I decided to read what other people thought of it. While most people gave glowing reviews, one person noted that how uncomfortable they were that, essentially, one character RAPES another character and then these two characters, after much remorse on the part of the rapist and forgiveness on the part of the victim, fall in love. Also, according to another review I read, the rape victim never gets to have a voice. OK, so the story is based on folklore and the victim is a nymph-like creature rather than an actual woman but I really don't understand how that makes that type of story acceptable. If the author wanted to raise the issue of redemption and forgiveness after rape, why didn't they tell the story from the rape victim's point of view? Obviously, the huge caveat is that I haven't read the book and I am basing my views on those of someone else rather than my own interpretation of book. But, nope, sorry, not prepared to give such a book a chance.
Back to the point in hand, as mentioned, I mainly read reviews after finishing a book. This is basically to see if someone agrees with my view of a book. I once went to an event where The Guardian columnist Tim Dowling was giving a talk. He said that most people only read columns that share or support their views - which pretty sums up my approach to reading reviews. That's not to say I don't read reviews that disagree with my view of a book; I just tend to keep reading reviews until I find one that does agree with me. (I might be shallow and egoistical in this respect, but at least I'm honest). I'd be very interested to find out how other people read reviews - so if you're reading this, let me know!
* = I hope my sister doesn't read this; she always takes the mick out of me for my inability to pronounce the word "specific"