I just discovered the Youtube channel “A British Audiophile” and it is so much better than everything out there that I feel like recommending it here. I have no affiliation with the owner.
Tarun is a very humble and knowledgeable person with an engineering background who explains things like speaker setup, room acoustics, cables etc. in the most comprehensive way. Content and delivery is just excellent. Absolutely top notch.
Even if you have set up your speakers already, check this out, for example: