Yes, yes I *do* have specific recommendations for how to approach this pile of more than thirty books. I would push the City Watch or Equal Rites novels on you. Or Small Gods, I liked that one a lot. Or the Death ones, oh crap now I am recommending the entire series. But I would steer you away from the first few novels at the beginning – the books became more confident and interesting as he went on. My favorite period starts at 1996. He or his editors make sure that any one of them is readable on its own. You could always go back and read the earlier ones later, once you've got the bug/consuming passion. It gets funnier once you know who Greebo and the Luggage are and have a little familiarity with Cripple Mr. Onion.
The stories are told in a very British voice. This is attractive to me, it might be less so to actual residents of the UK. (Though judging from his book sales numbers, they like it just fine.)
So titles. (God bless Wikipedia nerds for their comprehensive lists.) The City Watch titles: Guards, Guards! (– this is my favorite book title of all time) Men at Arms, Feet of Clay, Thud! , fear not, there are more. The Witches titles: Equal Rites, Weird Sisters, Witches Abroad, and again there are more. Death titles: Mort, Reaper Man, Hogfather, don’t worry, more of these too.
As I mentioned, some of my favorite books are the ones that appear starting in 1996 (Feet of Clay is great). I think Pratchett really starts writing his funniest and most coherent stories then. So that’s a fine place to start. There's only been one recent novel I didn't care for much: Monstrous Regiment. I didn't feel that the elements came together well, and the peacenicking was a bit deafening.
In summary I look forward to every book and I have a bunch of them on the bookshelf. I think of them in the same breath as Wodehouse: safe comedy by the numbers that includes a passion for language and transcends its ticky tacky components. I feel all out of breath now.
And here's a random internet tangent. I was reading Wil Wheaton’s blog today. (Recap: he’s sick and didn’t go to Penguicon last weekend, or the Star Trek movie premiere. You're welcome: I know you were on the edge of your seat.) He signed off “Less than three, Wil”. I figured this was one of those leetspeak thingies that youngsters know about. And some rudimentary research revealed that Less than three = <3 = heart =" love." Awww. Kind of too sweet but good to know the lingo.