Dear Li Ming,
English could be hard for you, since it is your second language. However, the way you learn could affect a lot. Firstly, the environment of your learning is definately important. Speaking in English will help you a lot. That is because you finally have the chance to have the freedom, using different range of vocabulary, try to use them yourself. In addition, reading could let you learn a major range of vocabulary. Books and magazines could be a choice, but you might want to read the news. News is a good choice, since the words used would be simultaneous to the words used daily.
With these suggestions, I hope you improve at speedy rate!
Best wishes,
Your Brother