Terry Pratchett virgin here. Where do I start?

You are in for a treat! He's amazing. I started with the first in the Discworld series and worked my way through. It's nice as he slowly introduces new characters and this way you get to know them all. But all books are fine to read as standalone a too and people definitely have their favourites so try a few or have a look and see which piques your interest and you can start with those. I love the City Watch, so the first one there is Guards Guards. The Witches are fab too

I'd start with Equal Rites - and concentrate on the witches books till you decide you want to explore more.

The colour of magic is fantastic but I'm not sure its the best book at all.

I’ve only read The Wee Free Men but it’s brilliant - parts of it have the kids and I rolling with laughter 😅

Ooh I'm so happy for you to come across him! It depends on whether you want to just focus on books with Granny Weatherwax in them or not.

The logical starting place would be 'The Colour of Magic' which is the first book in the Discworld series and go chronologically. If you're only interested in GW then you can probably start with Equal Rites and directly onto 'Wyrd Sisters'.

My all time favourite though is the Hogfather - I read it (and watch the adaptation) every Christmas .

Would also recommend 'Good Omens', which he wrote with Neil Gaiman.