I ran across this fine article on Lifehacker this morning.  It explains the steps to take on learning a foreign language in 90 days.  In a word, immersion.  Thinking, listening, reading, and speaking in the foreign language (with those who know the language, not who are also learning it) and learning new grammar and vocabulary for hours a day.  If your schedule and resources permit, it seems a solid approach.

Check it out!