Find an English-speaking person who is willing to spend time with you, just talking. Ask about any words you don't understand, write them down, and then try using them.
I totally agree with both previous posters. But, I don't think you can beat MM's advice to read, read, read! Read with a pencil and paper and a dictionary by your side. Jot down the words you don't know and the page number you found each on, so that when you look each one up, you can look back and read the sentences and paragraphs to see the word used in context.