What does it take to make you #review a #Kindle book?

I guess this is the eternal question that most authors would ask their readers. I've been trying to find out the industry standard rate for book sales on Amazon to reviews left, but the data is either elusive or does not exist.

It would be nice if it was 2% or even 1%, but so far I seem to get one review for every 300 or so sales. One of my books does a little better than that, but there's not a big margin of variation.

All my books feature a page at the end politely asking for a review or at least a rating, I've tried to persuade readers to leave a review in discussions on Facebook and Google+, and I've even given copies away free in return for reviews (which in the majority of cases did not lead to reviews).

Obviously, there are review sites out there, but I am dubious as to how a review generated that way would compare to one by someone who chose to read one of my books because they liked the sound of the story or read the sample chapters and wanted to go on and read the rest of it. I'm doubtful that someone who reads and reviews books in order to create content for their blog/website is as likely to enjoy what they are reading and write as positive a review. I've heard horror stories about authors getting bad reviews from people who didn't even like the sound of the book before they read it and then the resulting review damaging future sales.

I hoped I could get some of my friends to review my books, assuming they like the genre, but I've had no luck there either. Most of them are not big readers anyway.

So if you are a reader, what is the key thing which makes you want to leave a rating or write a review?