It is really hard and I understand you because I am in the same situation, but I think I have improved very much, so, I will say my experience:
1. You have to watch tv in English, specially, cartoons. At the beginning it is possible you dont understand any word or phrase, but, if you do it a lot of times, I promise you will understand better.
2. Think always in English. And you will discover that there are a lot words you dont know, so, search a dictionary and learn vocabulary.
3. Invent actual situations, for example at the airport, restaurant, school, and so on; and take all possible roles. I mean, you have to talk alone being customer, waiter, bellhop. It is a crazyness but it works very well.
4. Try to find an exchange partner and talk with him or her a large number of times.
With this, I promise you that your english will improve :D