Sometimes I see something in the weekly reading posts here that seems fun. I also try the StoryGraph recommender occasionally, but it often gives me a very narrow set of recs that I've seen 10 times already. (You can tell it not to recommend specific books or authors anymore, but I consider that a last resort.) Mainly, I look at a lot of lists (new releases, curated/themed, "similar"/"readers also enjoyed", etc).
Once I find something that looks interesting, I read a bunch of 3-star reviews on Goodreads or StoryGraph, to weed out stuff I'd be likely to drop. Whatever passes that test goes on my TBR.