Very good piece of advice. I won’t claim to have a very good vocabulary, but whatever words I know, most of them I have learned by making an extra effort of jotting them down in a notebook and then look them up. I remember when I was young my friends and cousins used to make fun of me because when I read a book, I also used to have the thick Oxford dictionary by my side.
You can add one more point here: use the newly-learned words as much as possible. It’s easier to remember words when you immediately use them. Make a habit of referring to the words you have noted down recently and trying to use them when you are writing blog posts and articles. Write five sentences of every new word that you learn.