How did you really learn a foreign language?
soc: I'm about 8 months in on learning Japanese.  I pretty much follow the method of alljapaneseallthetime(.com).  Learning grammer, kanji, and set sentences. An SRS program like anki helps a lot with these. Then just immerse yourself (tv, music, books, games).  Couple of helpful sites out there too (smart.fm, japanesepod101)