Shhh... Jon will hear you...
There's a lot of discussion on the proper reading order. Publication date versus story arcs. Problem is that even Terry Pratchett said that the first two novels (The Colour of Magic and The Light Fantastic) are not a good place to start. There are a couple of nearly standalone novels in the series if you want to get a taste without committing yourself to series.
Small Gods is a good place to start for a taste (and yes, the History Monks are in other novels, but the lack of background doesn't make this any less readable). One of my favorite books in the series.
Thief of Time is a good standalone and
Guards! Guards!, though it's the beginning of the Watch arc is a good book on it's own.