The best way to study for the JLPT or any exam for that matter,
is to try to take mock tests, check your weak points, study, test again, repeat until your test scores break 80% and above consistently.
My rule is that I should be getting 50% on mock test scores 6 months before the exam, and progressively improve on that. To do that, we can use books for learning the material and books specifically for testing grammar and reading.
For the vocabulary and Kanji, I just use online flashcards. No need to buy Kanji books or vocabulary books in my opinion. But, for the grammar and reading, that's where the books really helped me. Links to the actual books included below.
I took N2 twice, failed the first time.
The second time around, I had a better understanding of how to study and passed.
Reading speed is essential. Grammar patterns are essential. Listening is not that difficult, just get exposure. Vocabulary can be picked up from flashcards. Kanji is learned passively while learning vocabulary.
These resources helped me pass the 2nd time around...
1) Moshi to Taisaku N2 - I used this for N3, excellent resource. And used it again for N2, still excellent. Answer key has explanations.
2) Kanzen Master reading - for Reading, an absolute must! Must! Must! Answer the sample exams included with explanations for the answers. For N2, reading speed is essential so this is what I needed.
3) Power Drill Grammar - My favorite for grammar. 45 minutes per question set, not boring, learn to pace yourself perfectly!
You can take 1 Power Drill test a day and not get study fatigue. This is good for 0-3 months before the exam.
4) Mimi kara oboeru - book with audio, absolutely useful -> bombard yourself daily with the grammar patterns. I used the JLPT2 old version, still useful. The book contains additional example sentences not in the audio. Passive learning, just play the audio. If you want active learning, follow along with the text.
5) A dictionary of japanese grammar - very useful even after the JLPT, 3 books for lifetime Japanese learning. If something is not clear, it will usually be after you look it up in this excellent reference. Get the complete set -> basic, intermediate, advanced.
Sou Matome series (too easy, below actual exam difficulty) - I used these the first time and did not pass. :(
The classic Kanzen master is an absolute lifesaver. Answer the mock reading exam at the end.
Listen and learn! It's very sticky. Text comes with additional sentence patterns. absolutely useful, also helps with listening.
JLPT Try! is good for early on, around 3-6 months before the exam, for acquiring information. It covers listening, grammar, reading, vocabulary in one book. It's like an integrated all in one book. It's good but the exercises are too easy. I would still supplement it with a mock exam type of book.
My favorite for grammar. 45 minutes per question set, not boring, learn to pace yourself perfectly! You can take 1 test a day and not get study fatigue. This is good for 0-3 months before the exam.
5) A dictionary of japanese grammar
- very useful even after the JLPT, 3 books for lifetime Japanese
learning. If something is not clear, it will usually be after you look
it up in this excellent reference. Get the complete set -> basic, intermediate, advanced.