Book review blogs are a big deal. The most popular review sites have to charge to review book submissions if they even take them at all.
This is something you can leverage to get many book sales. Let me tell you how.
First, invest some time – several months at least. During that time publish good honest reviews of books you have been reading or have read in the last few years.
Second, when you have a good audience of readers following you, you are ready to go to step three. Like platform building as a whole, this step will take time.
Third, reach out to fellow authors with a reasonably sized following of their own. Offer them a simple swap – I will review your book if you review mine. Do this one at a time so you can keep up with the reviews.
This step gives you new books to read and review but also gets you a steady stream of reviews for your book. Encourage the reviewer to link to your page or subsite about your book as well as to your main website.
The links from those reviews will help readers to find you. Furthermore, links tend to raise you up the search results a little bit.
At the very least, each book review that your write will represent one sale to the other author.