Now what makes me a good demoman? Well, if I were a bad demoman, I wouldn't be sitting here, discussing it with you now would I! (ok I'll stop with the tf2 references) I say most since there might be some things I might leave out accidentally and if so, I would appreciate if you inform me of it and contribute to a more detailed and better guide.
This guide is meant to explain demolitionist mechanics as well as teach most aspects and techniques of the class.