Shelf-reading is an important part of stack maintenance. It includes reading each call number in order to ensure that the books are properly shelved. Patrons often place books back on the shelves without knowing exactly how to shelve books. It is inevitable that every worker will at some point accidentally misshelve a book. After a long day it becomes easy to loose focus and make simple mistakes. You should try not to shelve books or shelf-read when you are very tired.
Move through the stacks from left to right, and top to bottom by short shelves.
It is a good idea to take a quick survey of the shelves to get a sense of the physical extent of the alpha-range you're looking at so you won't inadvertently jump to the next subject letter. "LCC tunnel vision" often happens when scanning Cutters and losing sight of the entire call number.
Shelf-reading can take quite a while. It is more important that you take your time to be accurate than to rush through quickly and make mistakes.
After you have shelf-read for an extended amount of time, take a break. If your eyes hurt and you continue anyway it will lead to sloppy work.
Once again, we are more interested in making sure that the shelves are read precisely, not quickly. Do not hurry when shelf-reading.