This is my suggestion for starting out on the Sir Pterry journey because he has published a lot of books.

If you all get addicted to his books you can blame me later. LOL

The first one I ever read was Good Omens, and then I just kept ordering more and more of his books for the library branch I managed. Then I kept recommending them to library customers, friends, family, whoever I thought might be a potential fan.

I recommended them to an old school friend. Years later she introduced me to her teenage daughter and the way she introduced me was by saying, "Helen told me about the Pratchett books" and her daughter lit up like a Christmas tree. I'm guessing her life took a significant turn when she started reading his books.

The Colour of Magic was the first Discworld book, so it would be a good place to start just to understand the nature of that strange world. Then the other books could be read in any order but it might make sense of certain recurring characters or situations to read them more or less according to their date of publication.

Good Omens is not a Discworld novel so it can be read any time, and if you want to ease into it gently there is now a two-season TV series based on the book.

The other deceptively simple stand-alone book was Strata. It was one of his earliest books, before the Discworld series but not related.

Try them, you might like them. They are funny, clever, quirky. Unlike almost any other author I have read, except maybe Douglas Adams, author of The Hitchhiker's Guide to the Universe and also the Red Dwarf TV series, etc.