I am (still) learning English (and Thai and other languages). From my experience ‘interactive and repetitive learning’ (talking+listening/Q&A and getting ‘immediate corrections’ again and again) is best. Then grammar comes in to make understanding more exact between speakers/writers and listeners/readers.

Prof. Krashen presents a very high (meta) theory of learning that learners need not know but teachers should study and compare with their own teaching.