Libraries use classification systems to organize the books on the shelves. A classification system uses letters and numbers (call numbers) to arrange the books so that books on the same topic are together. Academic libraries use the Library of Congress Classification System (LC), which has 21 classes and over 225 subclasses, represented by letters.
Familiarize yourself with these classes and it will help you to find books and shelve more quickly.
Read call numbers line by line.
Image taken from The Online Library Learning Center website, a project of the Board of Regents of the University System of Georgia