Many books have been written on this subject… Different people have a preference for one approach over another.
While a few people seem to have the ability to learn a language from reading a book on the subject, there would probably be general agreement that it is hard to learn a language in this way. An audio course with cassettes or CD will work for some people. Others will find that Internet-based materials are effective.
Most people, though, will find that the above methods are secondary to the key one, which is interaction with an effective teacher. Language is a social experience, and we believe that it only really comes to live when it is used in a social context.