Having taken the N2 and the N1 multiple times each, I am pretty familiar with the test structure. It’s helpful to think of the JLPT as a basically a Reading and Listening Comprehension test.
If you know all the words, by sight and sound, and know how Japanese sentence structure works, you are in a pretty good position to pass, providing you have good test-taking skills. JLPT vocabulary has a pretty wide range — I had a 5-6,000 word Anki study practice, plus I do a lot of reading. Yet, there are always words I didn’t know on the test. Japanese just has a lot of words.
Grammar on the other hand, is a bit more finite. It begins with a solid grasp on verb tenses and particles (who is doing what to whom). Then come the patterns that make up most of the JLPT study guides on the market.
The good thing about the JLPT is that until you hit the N1, most of the stuff in the books is actually in everyday use in common Japanese settings. So besides rote memorization, you can also find usage examples in dramas, movies and books. I recommend a steady diet of media that corresponds to the level of test you are taking. N1 and N2 takers, for example, shouldn’t spend too much active listening time on anime. Rather, soap operas, NHK television, and movies that include everyday adult conversation should be on your playlist.
And of course, listen to this podcast over and over. Endlessly. Then 10 more times. The goal of grammar is not just another ton of stuff to memorize, but to get a feel for the flow of Japanese conversation, speaking, and prose.