>>534822918
You can mostly read it in any order, the more you read the more you realize how many locations and characters are recurring though so getting introduced to a character "the first time" will be different than a character showing up in the series for the twentieth time.
There's a few prominent characters and groups that have basically story arcs over several books so those are the only times starting at the "start" of a new group or main character being introduced is particularly useful.
I started on book #33, which introduces a Con Man who has been captured and put into Government Office to fix the Post so that mail doesn't fall by the wayside after the advent of huge light/flag signal towers sending wireless telegrams. In the next story he shows up in, #36, the same guy fixes up the banking system and mint.
But yeah just read whatever, anything focusing on Ankh-Morpork is a good place to start as that's basically the main recurring fantasy medieval london equivalent.