What method should I use to expand my vocabulary?

What method should I use to expand my vocabulary?

and how do I know if the word is commonly used?

Read a children's book. Typically, you will want to read the books that third or fourth-grade (3rd or 4th grade) children read. This will greatly help your vocabulary.

Be sure to have a dictionary. (I recommend an electronic dictionary; they're much more convenient.)

READ , READ and read stories magazenes english newspapers watch english cartoons and stick with oxfored dictionary. try to learn 3 new words every day and how they r used and u will see how your vocad increased adn expanded so fast and so much

GOODLUCK

you shouldn't memorize words, it's more usefull to memorize phrases..it's easier and more helpfull.and listen to childern's stories.