Comment by andrewla
I have a theory about language acquisition that I've never had the time to fully explore, that developing an ear for a language is the critical first step.
To that end, my theory would be that a program of imitation & mimicry would be the most effective way to learn. That you would hear a native speaker say a phrase and attempt to fluently imitate it. Specifically, record your voice as you speak and listen to what you say and try to as perfectly as possible imitate the prototype phrase.
Learn vocabulary and grammar later; focus, like children do, on hearing the language and imitating its use. Learn reading and writing last of all; formal grammar and especially spelling are the pedals on the bike.
That's the Pimsleur method. They have you listen and repeat sentences. You listen to a conversation between native speakers and repeat after them to practice the sounds and get a "feel" for it. Speaking is a physical thing with muscle memory.