I was introduced to Terry Pratchett via the witch books a few years ago - Wyrd Sisters was my first one. I think that is a good place to start. I love his stuff, and so does John.

I think I'm Nanny Ogg mainly, with a little bit of Granny Weatherwax thrown in.

I was reminded of Granny Weatherwax recently when there was a thread on here about being able to tell when a person is dead. When Granny Weatherwax went 'borrowing', her still appearance might have caused some confusion, so she always wore a small sign saying "I aten't dead".