When you're a writer, reviews can be a life force to your success. Good feedback leaves you dancing and encouraged to move forward, but even critical feedback helps you look at your work differently and address any flaws you can't see on your own. It's easy to see why authors should seek reviews, but there are some positive and negative ways to go about it. Submitting review requests is just like any other professional interaction, and should be treated as such.
As a reviewer, sadly I don't have time to review every book that comes my way. So personal preference will always be a factor. I look for books that fit my tastes, and I know many other reviewers do the same. For authors, this provides the first major hurdle to getting reviews: knowing the reviewer. If you want a reviewer to take to the time to read your work, than it is important to set aside a few minutes to get to know them. Check their recent posts, their to-read list, their top-picks. Does your book fall into any of these groups? Are the books they're reading ones you would pick up? When looking for reviewers it's not enough to just have someone who will 'give it a shot'. The most honest and helpful feedback is going to come from someone who loves books like yours.
The second big step is going to be writing a good request. It is more than just having a fancy pitch, or a good description; you have to be professional as well. Never treat your reviewer like you are doing them a favor sending in your request. While the book is free, they are still committing time to look at your work. Reviewers are just like other readers, and we have to discern what we choose to read. Time is valuable when many reviewers have other jobs, hobbies, and responsibilities. Requests that show you haven't read their policies, or that don't take time to include required information quickly show that an author doesn't care.
The third big factor to a successful request is to take care with your description. How you write your request is as important as how you write your book. A long winded explanation can turn off a reviewer and they may not move forward. Don't rely on your content alone to save you: you need to reviewer to want to open your book first. Be concise, be informative, and be polite.