As a university English teacher, I can tell you that what I'm about to say is pretty politically incorrect: Mastering grammar IS important. You might expect an English teacher to say that, but a closer inspection of our training and the academic environment that surrounds us will show that English teachers today come under a lot of pressure to ignore grammar. "The successful conveyance of meaning, that's the important thing!", the teacher hears all around. Well, I beg to differ. I learned German and speak it very comfortably today, and the way I did this was to focus on grammar -- German has three genders and four cases -- and as a result, I developed good habits right from the start. Today, my German is grammatically correct, not because I sit and contemplate the gender of every noun I use; no, it's because speaking properly (grammatically correct) is now habit for me and the only way I know how to speak German!