When I had my Library in the Lounge Room, my books were arranged alphabetically in Subject, then alphabetically within that subject.
It was always a talking point of guests, who used to 'thumb-through' them. I took that as a compliment! My subject matter was large & various.
I had no problems finding whatever book I needed for reference or reading.
Sadly, no longer in that house, so my Library is all packed up, probably never to be seen by me, or anyone else. I miss my books terribly. I used to sit in my comfy lounge chair & just look at them on their shelves. So relaxing to me!