I would first focus on syntax and grammar if I were you. I don't really think vocabulary is your problem. Ask a teacher or someone here on italki to explain English grammar and syntax for you. It will make your English much more understandable simply by being able to place the words in the right spot.

I think that everybody thinks like that to some degree, when they are learning a new language. Also - some ideas just don't translate very well - when you learn another language, you also learn another culture, and learn that other people can have different ways of thinking too. You are right that to some degree, a language is just a school subject, but the advantage of that, is that you remember the words so much better, when you are young. Also, from what I have heard, many Chinese English students don't learn to listen and speak English that much. If you can find a native English speaker to talk to, that would help you to practise your English, and also help you to understand other cultures too.

Actually you know, most common 1000 words are enough for daily life. you can search those 1000 words and learn their meaning or usage carefully. it may help you a lot. if you got more time, there was 5000 words needed for ielts. just learn those words. hope you improve soon...