I have not sat any of the JLPT tests so my experience may not be the most relevant, but my speaking and listening are JLPT1ish and I know all the words from the JLPT1 vocab decks.
I have never sat down and studied grammar directly. What I do is when I find a new grammar form I am unfamiliar with is immediately look up 5-10 example sentences, add them all into Anki, and work out the usage through osmosis. Grammar than starts to "feel right" or "feel wrong" as I am exposed to more and more examples.
I am not suggesting you throw away grammar study in favor of this, but it may help you to develop a more nuanced grasp of grammar if used in conjunction with your other studies.
I have never sat down and studied grammar directly. What I do is when I find a new grammar form I am unfamiliar with is immediately look up 5-10 example sentences, add them all into Anki, and work out the usage through osmosis. Grammar than starts to "feel right" or "feel wrong" as I am exposed to more and more examples.
I am not suggesting you throw away grammar study in favor of this, but it may help you to develop a more nuanced grasp of grammar if used in conjunction with your other studies.