Book reviews help your potential readers decide if your book is right for them. (They also help folks determine that your book isn't right for them, which helps your real fans self-identify.) The more reviews you have, the better your potential readers can determine if it’s a book they want. There are several ways to get book reviews.
One way is to be proactive and ask your readers for an honest review. You can include a request for a review at the end of your book – both in your print copies and digital versions. You might say, “Thank you for reading my book. I hope you enjoyed it. If you found the book useful, please leave a review on Amazon. Reviews keep me encouraged to keep writing.” Include a link to your book page so it will be easy for them to find it to review.
Another source of reviews is to ask those who have written a cover blurb. Once the book has been published, ask them if they would mind posting their review on Amazon.
On Amazon, find reviewers of similar books who include contact information in their profile. Reach out to them with a message such as “I saw you reviewed [title of book in same genre as yours]. I wondered if you’d be interested in reading [title of your book]. I’d be happy to send you a free digital or print review copy. I’d appreciate your honest review at Amazon. Thank you.”
There are other online reviewers and bloggers who review as well. If you offer to send them an ARC (Advanced Review Copy), they may be more than happy to post an online review or review the book on their blog.