The more words you're exposed to, the better vocabulary you will have. While you read, pay close attention to words you don't know. First, try to figure out their meanings from context. Then look the words up. Read and listen to challenging material so that you'll be exposed to many new words.
Research shows that the vast majority of words are learned from context.
To improve your context skills pay close attention to how words are used. Play our Daily Context Vocabulary Quiz. Learning a word won't help very much if you promptly forget it. Research shows that it takes from 10 to 20 repetitions to really make a word part of your vocabulary. As soon as you learn a new word, start using it.