In my opinion, the first thing should be to define what learning a language means. Some people think it only as being able to speak and understand in that language, some others will also go for writing or reading advanced materials. So we can say that how you can do it depends on what it means to you. Another factor could be the type of the learner. Some people learn by analyzing pieces while others learn by using and practicing. A last important factor that comes to my mind is the context. If you have the chance to live in the country where it is spoken, you'll be more exposed to the language and your speaking, listening and pronunciation skills will improve. But when you study the language, your grammar, writing and reading skills will tend to be better. Personally, I believe the best strategy is to know yourself and put the right pieces together in the right proportions... Hope this helps!