Sir Richard Burton is famous for (among other things) learning around 30 different languages, many of them obscure African and Asian ones, and developed a system whereby he claimed to be able to learn a new language in two months. I am currenty trying to apply some of his methods to improving my Arabic, after 4 semesters of lackluster college instruction. His basic strategy is as follows:
1) Spend a couple weeks memorizing 300-500 useful vocab words. He would carry word lists around with him and read over them carefully many times a day, limiting his study sessions to no more than 15 minutes.
2) At the same time, memorize some basic grammar rules. This would include sentence structure, possesion, and past, present, and future verb conjugations.
3) Train yourself to produce any foreign phonemes (sounds) by repeating it to yourself as often as possible until you get it down (in Burton's case, this meant thousands of times each day).
4) Obtain a familiar book in your target language. Burton used part of the Bible, but I'm hoping to track down some familiar children's books. Dictionary in hand, work your way through the text. When you encounter a new word, memorize it. When you encounter a new sentence construction or grammatical rule, look it up, make sure you understand it, and memorize it.
5) According to Burton, you should now be able to read, write, and speak pretty proficiently, and can therefore start trying to hold conversations or write, while continuing to devour whatever literature you can get your hands on. He also said that, when listening to someone speak, he would repeat their words to himself in order to internalize their rhythm and intonation. Today, we have the wonderful resource of foreign language TV and movies, so you can do this much more discretely.
I can't vouch for the success of this system, and I doubt it would hold much credence in a language classroom, but it does appeal to my sensibilities because of its high level of focus, and its emphasis on individual, self-directed learning.