collect all new words in a notebook

After using English-English dictionary to look up a new word, most of the students just write down the meaning near where they found the new word (For instance, text books, articles, newspapers) and can't remember where it is when you come across the new word again.

To efficiently increase your vocabulary, I would suggest ones to jot down all their new words in a notebook. With each new word, you can right down the meanings, the properties of the word, sentences containg this word to better understand it, etymology, and where you found the word. It might seems tedious to gather so much information for a single word but it's the invarient way to actually understand a word efficiently.

In addition, by collecting new words in a notebook, you're free of worrying about forgetting where it is and you can also have quizzes on your new words.