People learn in different ways. I'm sure there are a few people who decide to learn, for example, five new words beginning with A on Monday, and then five new words beginning with B on Tuesday etc. It doesn't seem very practical or helpful to me though. I am a fan of learning vocabulary as you discover each new word.
Please give the source of this advice about A-Z vocabulary (give us the title and author of the book).
Note my corrections to your post above, in red.
Student or Learner