The principles were as follows; books are first separated by hard back and paper back. Never should the two meet on the same shelf. Then books are arranged from tallest to shortest. The books should be slid out to the front of the shelves not placed against the back. Photos or knick knacks should not be on the same shelf with books, but if all possible placed on a separate shelf. The over all look is much more organized and there is the benefit of dust falling behind the books where it is not seen. No dusty lip in front of the books. However, I do miss the books being organized topically. It bothers me to not have all the nature books on one shelf, history on another. I might have to go back and see if I can't be more topical within this system. For now I think I will just enjoy the new look of my shelves!