Discworld

I agree that this guide isn't very easy to follow. It also seems to be attempting to show additional subseries like "industrial revolution", which is sort of an ongoing theme across different subseries but not necessarily something that stands on its own (I would consider Moving Pictures or The Truth more standalone books). Or the history monks that pop up in several scattered books but aren't exactly major characters for the most part. That said, there's not exactly a wrong place to start so long as you're willing to give the first few books a little leeway, somewhat like the first season of a longer TV show.