There’s really only one “rule” for building your vocabulary:

“Use it or lose it.”
When you are learning a new word, if you don’t use it, you will soon forget what it means. Write new words down on a vocabulary list or in a notebook. Use them in emails or text messages to your friends. Introduce them to members of your family.
Use the words you learn in your everyday communications as much as possible so they become a permanent part of your vocabulary.
“Use it or lose it”