i worked as a librarian for multiple years and can't think of a good way to improve on the systems already in use, honestly (at least on the physical side of things; library software is almost always horrible horrible, and any suggestions to use something better is denied because the peeps in charge are all in their 60s and Know Best, so you're stuck with using failing, 15-year-old machines running xp to run a laggy, constantly-timing-out remote desktop into a virtual system halfway across the globe running windows 8.1 and this garbage: https://www.iii.com/products/polaris
on the physical side of things, though, we had fiction sorted by author and non-fiction sorted by topic, as those are how just about everybody looks for them. we also had genre tags like you've described in the fiction section to make things a bit easier for people scanning for that and, just as i was leaving, were in the process of giving every book a unique rfid tag, meaning a book could be scanned for on a shelf with a quick gun once-over: impossibly helpful when looking for misplaced books.
also, the two biggest threats to a well-organised library are thieves and highschool shelvers who purposely put things back in the wrong place to finish up more quickly, with third and fourth going to the homeless people shooting up heroin in the bathroom and then swapping things around at random and fricking bed bugs coming in through the book drop.
bed bugs; just ugh X_X