I have around 50 books in my TBR pile. I maintain a hunting list of books that intrigue me from postings on this site and other random sources. The list is a combination of works by favorite authors and new ones to try. When I identify a new series, I try to collect the first 3 books or so before I begin reading it. My hunting list typically has between 25 and 75 titles. I use the list on periodic visits to used bookstores. So far, this approach provides a good selection of books to read at a reasonable price.
Selections for reading are a combination of method and random madness, but mostly random madness. I’m working on reading all of the Hugo and Nebula winning novels, so I try to pick at least one of those a month. I also like series, but I do not read them back to back. When I finish a series book, I typically read 2 to 4 other books before reading the next in the series. After 3 or 4 books in a series, I may take an even longer break before returning to the series. Otherwise, my reading selections are based on whims at the time. Sometimes, I want something similar to what I just finished. Other times, I look for something with a big change of pace or style from my last read.