We as librarians know how great our collections are, but often collections don't see the use they probably deserve. A combination of physical displays, social media and traditional media presence, and tying in programming are good ways to market fiction collections and increase circulation.
Physical displays are a great starting point to grab your users' attention. Use color, humor, and tie-ins to create fresh, flexible displays. In 20 Rules for Better Book Displays, Susan Brown recommends displays based on popular culture, current events, jokes, and anything that "reflect[s] your patrons' interests (2013). Chris Rippel recommends taking a page from bookstores in designing space to accommodate large displays and allow judicous browsing. "Librarians should observe how patrons move through [the] library" to determine where displays should be (2012).
Physical displays are limited to the geography of the library, therefore engaging social media platforms is a must. Many libraries post photos of displays or reading lists on Instagram, Facebook, and Pinterest. It's a quick, continuous way to market ever-changing collections and interact with potential readers.
Traditional media is another way to promote collections. My local library publishes new books and the month's highest-circulated books in its largest local paper. I know this is effective because at the library I work in, we often help patrons find the books the read about in the adjacent city's paper.
Finally, programming built around collections promotes usage of those collections. Book discussion groups from traditional book clubs to genre lunches, where attendees meet over a lunch hour to talk about what they're reading in their preferred genre. Book clubs may also be run online though Goodreads or Facebook. Libraries can also host author talks which promote both works by that author and read-a-likes.
Brown, S. (2013). Twenty rules for better book displays. Novelist. Retrieved April 20, 2017, from https://www.ebscohost.com/novelist/novelist-special/twenty-rules-for-better-book-displays
Rippel, C. (2012). What libraries can learn from bookstore. Web Junction. Retrieved April 21, 2017, from http://www.webjunction.org/documents/webjunction/What_Libraries_Can_Learn_from_Bookstores.html