There are many ways to improve our English level. Obviously, to learn this language the solution could be going to other country where you practice it, England for example, but so many people can't afford it. So, what can they do? For this reason, reading books and watching films in English is advisable to everyone, because you would have the possibility to get more vocabulary besides of having a better pronunciation. 
At first, it will be difficult for people who don't know English, but if you practice these habits, it will become easier. You can watch your favorite film or TV series with subtitles in English too, to know how to write words. Also, you may use a dictionary when you don't understand something. 
On the other hand, the trouble  is when we put subtitles in Spanish, and you usually look AT THEM MORE. It isn't useful. In addition, there are many expressions that are unknown to us, so you won't know what it means.
To sum up, things as simple like that would help us to improve this language so important.