How much does knowledge of linguistics help with learning foreign languages?

[Astreja]

I don't think that knowledge of the nuts and bolts of a language is necessary to become reasonably fluent, although it would definitely help you do higher-level writing in that language. Think back to childhood, when you learned your first language: Unless you lived in a very odd household, chances are someone didn't lecture you on phonemes and declensions and such -- they just spoke to you, and eventually you made a transition from speaking to writing.

Personally I think that immersion (travelling; watching and listening to shows in a language, reading websites in a language) is the best way to learn to speak with native speakers.