Mainstream fiction is a generalized genre that encompasses many different types of fiction. Mainstream manuscripts are between 60-90K words.
Defining what “mainstream fiction” books typically entail is completely dependent on the type of book you’re writing for a general audience. Imagine walking into your local Barnes & Noble (or other large bookseller) and you bump into the table of current bestsellers and other big names in fiction. The specific genres might be different, but they all have in common that the authors are recognizable, or the books are appealing across audiences. Many of the books that Oprah selected for her book club are considered mainstream fiction. If they weren’t considered to be general in nature before she selected them, they probably became mainstream fiction afterwards. These are also the books sold in stores such as Target, where the selection is not that large or categorized because the store isn’t a book specialist. It just clumps them together on a couple of bookshelves.
Current authors of mainstream fiction include Charlaine Harris, whose Sookie Stackhouse series was adapted into the hit show “True Blood.” She would have been considered a sci-fi/fantasy/romance author up until the moment her book was adapted. Now, however, she’s a recognizable author across genres and her books have become even commonplace. James Patterson deals mostly with the suspense genre, yet his books fit the mainstream genre well. Nicholas Sparks is a women’s fiction author, and his stake in the mainstream fiction market comes from the sheer volume of books he produces, and that he seems to always have a new release and something on the bestseller list.
The principal characteristic of mainstream fiction is that it is essentially literature accessible to people across all age groups and gender lines. The books must have an appeal for everyone if they are to be considered mainstream.