One option is to post excerpts from your novel on your blog or a third-party platform like Medium. This is a little more difficult in fiction, but it is still possible. Another option is to publish a short fiction including some of the characters from your book. Readers will have to purchase your book if they want to learn more.
Connect with Influential Reviewers:
Research some of the most-wanted and top reviewers on Amazon, Trustpilot, and Goodreads. Concentrate on folks who have written a lot of book promotion services reviews in your niche.
Get a feel of a reviewer's preferences before contacting them. You'd want to send your book to someone who will like it. Send a concise and courteous note offering to provide the reviewer a complimentary copy of your book in exchange for a review. You can also contact the local newspaper and specialty magazine reviewers.