I speak three languages and I'm learning a fourth. Don't study grammar, ever, it's a waste of time. Grammar rules always fall into one of two categories: the ones that are so obvious that you would have learned them after two examples anyway or the ones that are too vague and complicated to be useful. For an example of the latter look up people making flowcharts for the subjunctive or for the ga/wa distinction. Or, for that matter, find me the place in an english grammar that explains why you get "on" a train, but "in" a car.