I would suggest you read newspapers, books and articles in magazines. When you find a word you don't understand - look it up in the dictionary.
This goes for movies too... but they tend to be a little fast moving and you may forget which words you don't understand.
I still do this myself, and I'm English!! I keep hearing the word "hubris" in movies and games - so I looked it up.
"Excessive pride or self confidence"
I also keep forgetting what the word means!!