There really isn't a wrong order, in my view. Although reading them entirely in reverse publishing order, say, might be confusing, it would probably still be enjoyable. And I know from experience that using whatever-I-find-in-used-bookstores order can work out just fine.

Yeah, they're pretty good about getting you up to speed. I think the Tiffany Achings are actually a great way to start.

Although reading them entirely in reverse publishing order, say, might be confusing.

This is kind of what I did. My first book was Thud when it first came out, then I went backwards through the Watch series until I got to Guards Guards, after which I went backwards through the Industrial thread (starting with Making Money). This was mostly because those were the books I had on hand when I started reading Pratchett. OTOH, I did the Death, Rincewind, and the Witches threads in proper order... Mostly. Now I'm going backwards through the Aching books.

It's probably well that I did it that way, because I think that if I had started out with the Colour of Magic I wouldn't have continued.

One of my friends feels strongly that I should start with Guards Guards. I'm a complete noob and have no idea where the best place is to jump in.

Also, there's this:

The Discworld Reading Order

which is a simple graphic showing the various groups of books.

Yes, reading the Guards books in order is a great deal of fun, watching the progression of Sam Vimes.

One of my friends feels strongly that I should start with Guards Guards. I'm a complete noob and have no idea where the best place is to jump in.

That is a great jumping point, as Connie says. I did the Guards books in order a couple years ago and it was awesome to see Vimes and the Watch grow and change. I think if you start by doing all those books in order, you get a strong backbone for Discworld since they're ones where Ankh-Morpork is a character in and of itself.

Also VETINARI.

I think I read Pyramids first, which was a good place to start, and then whatever I came across until I happened upon The Colour of Magic at which point I started going through mostly in publication order as affected by availability until I caught up and had to wait for something new to come out at which point I, of course, read in publication order. Worked for me, but would be hard to recreate exactly.

Guards Guards is a good place to start. I'm partial to the witches in general. You could make list of what would be easiest to get from your library and throw a dart at the list, read whatever title it hits.

Or you could read Nation which isn't Discworld at all but is great. While you decide where to start with Discworld.

I still have a pile of library books to get through first (Cherie Priest's second Lizzie Borden book, Chapelwood [which I got stalled on when I got Jenny Lawson's new book]; Libba Bray's second Diviners book, Lair of Dreams; a book about caring for elderly dogs (god damn it); and Dietland).

...I have a book problem.

I'm also deeply resentful there are no more new Harry Dresden books for now.

A book problem or a book opportunity?

And if you figure out what kind of opportunity that would be, let me know, as I may have it, too.