speak english fluently

Hello. I like English a lot, and I can say that it's inseparable part of my life. I try to watch movies, listen to musics, speaking (a little) ,and read books in English to promote my English as much as possible. But to tell the truth, most of the time I cannot use the new words which I've learned. How can I learn slang and informal speaking? Do you think that participating in private classes will be useful in order to improve my English speaking level?? What do you recommend for me about speaking? Thank you very much