A successful ebook promotion begins with reaching readers who are genuinely interested in the type of book you have written.
The Fussy Librarian uses genre preferences and other reader information to help match books with relevant readers, but several factors outside the newsletter can also influence results.
These may include your cover, book description, genre, reviews, price, retailer availability, series position, and the strength of the book's retailer page.
Your goal also matters. One author may define success as generating a large number of free downloads, while another may care more about paid sales, series read-through, reviews, or introducing a new author name to readers.
For that reason, it is better to evaluate a promotion against your specific objectives rather than relying on a single benchmark for every book.