Luckily, I have a writing community that was extremely helpful and steered me in the right direction.
Some basic facts:
1. Publishers use comp titles as a gauge to show how well new titles might sell.2. Use Amazon to start your search. Look for books that are similar to yours in subject, genre, age group, fiction or nonfiction. You can also pick the brain of your local librarian. Ask them if they know of similar titles to your book.
3. Don’t use bestsellers as a comp title. Chances are your book will not be a bestseller and you should look for modest-selling titles.
4. To find modest-selling titles, use Amazon to find similar titles and check the reviews. Bestsellers can have hundreds of thousands of reviews, modest-selling titles may have less than 1000.
Bonus link written by Star Wuerdemann, How to Find Compelling Comps for Your Book plus tips from an agent and QueryShark.