Living Abroad
If you really want to become fluent in a language, nothing beats living in a country where it is spoken. Then you'll learn every day, from talking to people, listening to the radio, watching TV, reading posters, papers and cereal packets. Total immersion!
The language environment
Learning a language through courses or teach-yourself materials can seem like a hard slog through the remote dusty landscape of school and academia. But languages are vibrant, living things, and they deserve to be seen in their proper natural environments. This is the best way to learn a language: spend as much time as possible in a country where it actually lives. Your absorption of vocabulary, grammar and phrases will increase exponentially just through daily experience - through meeting people, getting about, shopping, hearing announcements, looking at advertisements, reading papers, listening to the radio, going to the cinema.
The rhythms of language
Simply be being abroad and engaging in daily life, you'll begin to master the greetings and ritual exchanges that make up so much of communication, and oil the wheels of conversation. You'll rapidly gain an instinctual feel for the structure and rhythms of the language, which will enable you to make the right choice of words without even having to think about it.
Courses abroad
If you cannot live abroad, you could try following a course abroad for a week or two. To be fully immersed in the environment of the language both inside and outside the classroom will be an enormous help.
Virtual immersion at home
You may not be able to spend any time abroad just now. But back at home, you can replicate some of this valuable experience by buying magazines and newspapers in your chosen language, and by watching foreign-language films and TV network programmes. Look for material that relates to subjects that intrigue you: pop music, celebrities, sport, whatever. If you can find a radio station that broadcasts in your chosen language, put it on when you're in the kitchen or driving a car. Or look for radio stations online. You probably won't understand everything, but don't worry: you'll get an ear for the accent, and for the rhythms and 'feel' of the language.