Usually the best way is to "add" some english to your everyday activities. If you have a hobbie, like singing, or you like to spend your free time watching tv shows, youtube videos, etc you might as well do it in english. It was easier for me this way since you don't have that pressure of having to learn the language via books and exams.

You should read books 

I'd turn the subtitles on. Except use English subtitles. It will also help with listening. It is something that I've been doing with Korean. I'll watch Korean movies, with Korean subtitles.

Don't worry, that lack of vocabulary comes with time, the fact that you understand the general meaning is a good sign. The media usually use an "intermediate" english, not too formal neither to casual, in tv shows and movies there are some words that don't appear in regular dictionaries. So I recommend looking for those word in urbandictionary.com, it's a useful tool.

If you have the level to understand those series you should start talking on forums with people, and as Charles said, keep conversations, that way people can correct your mistakes in real time, and you get used to the tone, the expressions, etc etc.