I kind of feel that you need to read the Colour of Magic to get a proper introduction to the Discworld itself though (just ignore the story though, it's rather flimsy), but it might not be necessary to read it first.
I honestly wouldn't recommend it as a first book - and I appreciate the TV mini-series that collapsed Colour of Magic and A Light Fantastic into a single coherent story.
Also, it had Tim Curry.
But the discworld doesn't actually need all that much introduction - each book is pretty self-sufficient but learning more about the characters just adds more to when they show up as Cameos (except, I'd point out, Monstrous Regiment, where not knowing who the "Butcher of Ankh Morpork" is actually adds to the story)
