Reading books, listening music, watching films are really helpful but the most important thing that I think extremely can speed up your learning is to be on touch with a native speaker who honestly care and seriously devoting time to you.

I think learning a language should be in a systematic approach, I assume my brain is such as a computer which has input skills " reading & listening " and output skills " writing & speaking ". As much improving the listening and reading skills as much better I can perform the writing and speaking skills. To develop my vocabulary, how to keep and use it perfectly, is important for speaking and writing skill. Finally, practice with a native speaker or a teacher is required to correct my mistakes and support me master my skills. This is just my perspective to learn or teach a language, maybe I ignored main elements. I see this subject needs someone who has great experience to give much benefits, doesn't it!  

Do something that you like in that language, as reading a book, watching a film, playing a videogame or listening to songs as izabella does!

I've been spending time doing that kind of activities in English and I have improved since then! all while having fun!

I like learning languages through singing :D I listen to music (in foreign languages, of course) and I usually sing with the singer although I REALLY CAN'T sing. I found this really cool song in Spanish and now I can't get it out of my head... And I listen to Japanese music all the time and I know the lyrics for many japanese songs (even though I have no Idea what I am singing about ;-; but I've just started learning Japanese so it's understandable). It's fun! Give it a try!

Fun activities and games.