From my own personal experience, I'd say that the best way to learn a new language fairly late in one's life is to live with someone who speaks the language (roommate, girlfriend or boyfriend). I moved to Toronto in the 90s without knowing much English. The first year was rough... I managed to learn the language over the years, but it wasn't until my (English speaking) girlfriend and I moved in together that I truly began to gain a respectable fluency level. This was true immersion, metaphorically and literally speaking