There are, of course, a large variety of ways to market a fiction collection and no one way will fit every library. Each library has its community and readers that have their preferred ways of finding reading materials. So these are just a few of the ways we can promote our collections.
Social Media
While it may feel a little passive at times, social media is an excellent way to promote a fiction collection. My library has a number of things they do on their social media pages to market these collections. They regularly post a "What are you reading?" prompt to invite patrons to share about the books they're reading and interact with each other - many will often share a little of what it's about or what they like/don't like about it. For National Library Week, they posted about fiction titles that revolved around libraries while linking to staff lists on the library's catalog site. Other staff lists are often shared, as well. They've recently begun working on getting more staff picks involved in the creation of social content (I was semi-forced into making a silent reaction video for TikTok about fantasy romance novels (the pains of working next door to the communications department and being friends with them)) that has garnered attention from patrons for more content like it. They'll also occasionally do a "give us a book and we'll give you your next read" type of posts, involving librarians and giving patrons a glimpse into readers advisory.