Dear Melanie - you publish a book that is a compelling read in a hot selling genre/subgenre, or niche. People buy the book. They are gripped by it, page by page, sentence by sentence, word by word. Even after they have finished reading the book, it lives in their imagination, and they are enthused by it, and this makes them want to write a review, to express how wonderful they thought the book was, and share their enthusiasm with others. This is how you get reviews...
However... you say that reviews help your ranking. This is incorrect. It is also incorrect that reviews help with sales. Reviews - and I am talking genuine reviews, not friends, family, bought, paid for, or any other such scammy shenanigans - come after the vast majority of sales have been made. A book is published. If it is going to sell, then it sells. It takes time for people to find the book, then decide they're going to buy the book, then read, then reflect, then write a review and upload it - and this happens long, long after the fact. What I am trying to say is that reviews are the consequences of sales, not the causes.
However again... there are reviews and there are reviews. There are those reviews that enthuse, and whisper sweet nothings to your ego with a constellation of five glowing stars. And then there are those other, darker reviews that twinkle their one solitary little star in the long night of your soul, and eviscerate your cherished masterpeice more cleanly than if it had been laid out on a butcher's slab. And what I am saying here is the old but still relevant chestnut of beware what you wish for for it might come true...
So... the long and the short of it is that you don't get reviews. They get you. And they either get you good or they get you bad.
And their ain't a whole heap you can do about it one way or t'other.
I've been a writer for six years now. I have had many readers along the way. Most never even left reviews. I'm really interested in people reading my work, but I also just enjoy writing. I learned that it's so much better getting readers than getting reviews.
I had some very ugly reviews at the beginning when I first became a writer and this just turned me off from reading the reviews. The reviews had nothing to do with the books and all they did was cursed at me and called me ugly names. So what I do is just write these days and enjoy it very much. Great success on your work. Congratulations.:-)
I might add to Melanie's good post that most "reviews" on Amazon are not really reviews. I was fortunate enough to have a couple of readers take up most, if not all, of my 20 mystery novels and write several paragraphs on each. I suppose even the one liner reviews have some value, but ask yourself--have you ever bought an ebook because some readers put up one-liners? even 5 star one-liners? I know I haven't. Perhaps a few do.
Getting eleven reviews for over 100 copies is actually good going - most readers never bother.
It is a slow and frustrating process but there are legit ways you can increase them organically. There are also quite a few dodgy ones (review swaps or paid reviews etc) which might get you banned.
Boost your visibility by marketing - the more copies you sell, the more people who might leave reviews.
A professional product (cover, blurb, formatting) = more sales = more people to leave reviews.
Paid advertising might work for you (leave it a few weeks until the recent glitches with AMS are resolved).