Right, so, here is the Wikipedia entry on the Discworld books. It is mildly terrifying; there are 39 of these novels, which is kind of a daunting prospect. Luckily, these books fall into a number of different…mini-series, if you will, and luckier still most of them can be read alone. The way I figure it, there are a couple of different paths that you can take to get into these books. I shall lay them out below.
If You Are A Single-Character Driven Reader:
So! There a couple different paths you can take if you’re the kind of reader who tends to imprint on one character first and the world/plot/other characters around them second; I’m going to strongly suggest that you attach yourself to either Sam Vimes or Susan Sto Helit, since I feel like the two of them, in addition to being great characters, are the two mains whose paths do the best job of introducing you to the assorted cast of characters that make up the Discworld.
Which, okay. The thing about these novels is that they’re very…Pratchett approaches worldbuilding using the “Here’s the world through the eyes of folks who’ve known it forever, keep up!” method, and he does so very effectively. And part of that is because, while every book has a given focal point or set of focal points, the characters who make up the Discworld drift in and out of each others’ stories at will. Occasionally you catch one of the wizards in a Watch book! Vetinari’s tentacles go everywhere (he does not really have tentacles, though some characters do, on the Disc)! Fred Colon and Nobby Nobbs just appear places! Foul ‘Ol Ron says “Millenium hand and shrimp!” And Death will invariably show up somewhere, stalking that stalk and TALKING THAT TALK, as will his granddaughter Susan. Speaking of which: