Let's say you've heard of this "funny fantasy series" called Discworld by some guy named Terry Pratchett. You've never read any of the books, but you're intrigued. Unfortunately, there are a lot of books in the series and there doesn't seem to be an obvious book to start with. What should you do?
I'll tell you what you should do: read Small Gods. Many of the Discworld novels are tied to one story arc or another, but Small Gods is independent. (The only recurring Discworld character in the book is Death, but you don't need to have read any other Discworld books to be familiar with Death. It's Death. We're all going to have to face him eventually.) Small Gods tells the story of Om, a once great deity who has been incarnated into the relatively powerless body of a one-eyed tortoise, and Brutha, an eager but not particularly bright religious disciple who can hear Om talking in his head. When the two of them get together, they set off a strange and hilarious chain of events involving politics, conspiracy, holy wars, natural philosophy and science, and one very hungry, determined eagle. Pratchett's Discworld stories are cynically, wickedly funny but with a warm, optimistic humanism at the core. Pratchett uses comedy and stock fantasy tropes to examine broad issues and contemporary problems. I firmly believe the Discworld books as a whole are one of the best series in all of literature, and if you need a jumping-on point, Small Gods is a great way to start.