First, "vocabulary" is uncountable; it's an unmeasured collection of countable words. "How does one enrich their vocabulary?"
The basic answer is to USE the word. Write or copy a few sentences which use that word. If it seems similar to another word, then take a moment to work out the difference.
Learn ABOUT the word. If it's a long word, how does it break down? Is any part related to other words?
What comes into your head when you think of the word? What is the "feeling" of the word to you? Even if it's a silly image, you have more chance of remembering it that way.
Yes, this may seem time-consuming, but it's far more guaranteed that you will remember the word this way instead of reading the definition and thinking you'll remember it.