Learning a Language Intensively
Without a doubt, there is no more effective or efficient way to learn a language than to do it intensively. It is possible to learn a language in a surprisingly short period of time in this way. What do I mean by intensively?
First, we're talking about a serious time commitment. At least two hours, or up to four or more each and every day. At that pace, three to six months is a reasonable time frame to learn a language to a significant level. It doesn't have to be two hours in one sitting. In fact, breaking up that time each day into smaller, more manageable, chunks throughout the day is actually better.
Although most people would initially say "I just don't have that kind of time," I think some review of your daily schedule might reveal that you actually have more time than you would think, especially considering that learning a language is different from learning other subjects. If you factor in time commuting to work, doing chores, shopping etc, a great deal more time opens up, especially if you vary your learning materials, which brings me to my next point.
Secondly, learning a language intensively requires using a variety of methods, learning tools, and techniques. Your routine must be holistic and comprehensive, practicing the four traditional language skills of reading, writing, listening and speaking through doing different activities. This means studying grammar, reading, listening, practicing pronunciation, learning vocabulary, reviewing frequently, and using techniques such as spaced repetition programs and shadowing. One language course simply won't cover all of your possible needs if you're going to do it right.
Varying the methods and techniques you use will create synergies that one course alone wouldn't. This creates opportunities for the brain to recognize and absorb the patterns involved in learning a language. Seemingly constant exposure to this new information will create an immersive environment for yourself. But it requires discipline, planning and some effective goal-setting.
I think that we tend to think that learning is almost entirely a conscious mental process, when in fact much of it (if not most) is actually happening unconsciously. Learning a language intensively gives the brain maximum opportunity and a sense of urgency, and that results in a more effective and efficient language learning experience.