You can read more books or listen to English TV/radio.
Furthermore, you can go to TST to talk with English native foreign people. If you can practice English for 1 or 2 years, I think your English can be improved further.
Here is an easy three-steps approach for you:
1. Read: Read different types of books and articles.
2. Keep a list of vocab: Keep a notebook for vocabularies that you do not understand and would like to learn. When you come across a vocabulary that you do not understand, write it down in the notebook and check the meaning. It would be better if you could write down what form of words they are (i.e. nouns, verbs, adjectives) and write down synonyms and antonyms.
3. Write: The more you write the better you are. Start off by writing journals; write down whatever you want. After a while, start to write essays. Remember the basic rule is:
a. Introduction (1 paragraph)
b. Body (3 - 7 paragraphs)
c. Conclusion (1 paragraph)