I think the books on the shelf should be classified and put together according to the nature of the books, which will be very convenient to find. However, most people usually make trouble in the future for temporary convenience. In fact, I think each layer of the bookshelf may need to put different types of books. For example, I will make a classification on my bookshelf, and the nature of the books on each bookshelf is different.

I think the so-called neat arrangement is not just vertical or horizontal. I think the two ways can be combined, and usually this way can look more tidy. Mainly according to the nature and labeling, the types of books placed on the first floor are posted on the shelves on the first floor.

Perhaps this arrangement is clearer and neater. Books on the first floor can be placed vertically, and books on the second floor can be placed horizontally. In fact, this is mainly the size of the reading shelf, so it is good to make maximum use of the bookshelf.