Native language is English, French and Spanish in high school. German and Russian in university. I can read books written at an adult level in French, high school level in Spanish. I've used French in sales meetings with customers in Paris, and once I even presented a solution in French on my own. Learned German to an advanced level through company lessons (in London) and podcasts from Deutsche Welle. I am almost fluent in Russian, have traveled independently in Russia and Ukraine, romanced a girl on the phone in Russian, then visited her and ultimately married her. I say almost fluent because although I can watch Russian films and TV, I stumble with business/work scenarios. 10 years ago I was at the "almost fluent" level with Spanish after living in the Bay Area, CA, listening to hispanic radio on my commutes, reading the free Spanish language newspapers, and chatting (or ordering) in Spanish in every shop or restaurant that I visited. I am also competent enough in Italian to have traveled independently in Italy twice, once without even reserving a hotel in advance. I also spent two weeks in Bulgaria and was able to find a bus and wander around the town of Varna, shopping and visiting museums, all on the strenght of the Bulgarian I learned in the month before travel and by reading books (and listening to people) during the two weeks.

Why the long song and dance? Because I did it and I know how to do it. It is actually quite simple and is obvious if you think it over a bit. You have to work at it EVERY day, 365 days a year. Spend an hour or more a day. Find ways to extend that time whenever you can, for instance turn on the Spanish audio on a DVD and English subtitles instead of watching TV in English.

Second thing to do is to exercise all of the language senses EVERY DAY! If you sit down with a language book and spend all day Saturday on a couple of lessons learning them by heart then you are doing it wrong, wasting your time and will soon drop the studying entirely.

Every day you must read some of the language. Every day you must write, preferably full sentences or phrases, not just vocabulary words. For instance if you learn that sombrero means hat, then write "El muchacho no sabe donde esta su sombrero" or at least "un sombrero blanco" at the very minimum.

Every day you must listen to the language. In some countries there is easy access to TV or radio signals, but everyone who can read this can download podcasts. Listening to the CD that came with a course does not count. Sure, do listen to the CD, but don't check off listening until you listen to some language in the wild, so to speak.

Every day you must speak the language. In the beginning you can get away with reading a page out loud even if you don't understand the words. But preferably you should be speaking with native speakers. I get a free newspaper handed out every morning outside the transit station by a Chinese guy so I always say "Xie xie) which means thank you. When I took my daughter to a birthday party and entered a room of Chinese girls I said "Ni men hao" which means hello everyone. Yep, I am working on yet another language since I live in China now (the North American part commonly called Vancouver BC).

And you must also spend a reasonable chunk of time everyday talking to imaginary friends entirely in the new language. Don't speak out loud, but hold the conversation in your head as you walk to the subway, or take a lunchtime jog. Often you will not be able to fully express your thoughts because you lack the vocabulary so practice describing what you want to say. For instance, if you don't know the word tree but want to say "See the bird up in that tree" then try saying "See the bird up in that big plant, the really high one beside the park bench. What is that called?" When you get advanced enough, that kind of mental maneuvering will actually help you recall words that you had once learned but half forgotten.

Don't fuss over courses. Go to a good bookstore with a wide selection and browse through the books. Buy one or two whose writer seems to write in a way that you can understand and will not get bored with. When you are more advanced look for specific types of books. A comprehensive dictionary. A grammar book. A vocabulary builder book.

Buy some books written for 8 year olds in the foreign language. Stick to books written by a native speaker of the language where the action of the story is set in a country where this language is spoken. Especially avoid books originally written in English that were translated. When you can get through one of these, buy some books for 10 year olds, then 12, then 14 year olds. After that go to adult books. The age thing is important because young people do not have large vocabularies. Therefore childrens' book editors spend a lot of time editing books so the child will learn the meaning of new words from the context. You will learn them too and save much time that would have been spent with the dictionary.