If a unit library wants to be professional, it can refer to the Chinese Library Classification, which is not complicated and easy to master. Its greatest advantage is standardization. Just write the classification number on the label (1 letter+three or four numbers).

If it is a general classification, just think about what criteria to use for classification, such as specialty, book title, author name and so on. The classification system should not only be comprehensive to prevent omissions, but also be easy to find records.