I think there are 42 books, so it is a lot. I put it off forever, but started this year with Guards, Guards (#8) and loved that, then did Mort (#4), Equal Rites (#3), and then figured I better start at the beginning since I seemed to be invested.
Someone had told me The Hogfather live action movie was on YouTube, and I watched that last year before reading the books, and was a bit lost on what was going on, but still enjoyed it.
I'm on Pyramids (#7) now, and while they all seem rather self contained at this point where you could start anywhere, Guards, Guards is a good place to start if you prefer a crime story centered around dragons, or Mort to get a solid into to Death, who generally at least has a few pop-ins in each story.
Lore feels well established, but not deep, so it's not intimidating to learn how this universe works, and if something seems unusual like an orangutan librarian, don't expect much deeper of an intro than that, he's cool with it, so people just leave him to his books, so why should the reader question it deeper than that? It's just fun to read for the sarcasm, wit, and funny events, nothing to be taken seriously.