Sou Matome

This series and Kanzen Master are maybe the two most popular set of study guides. I personally like this best, even though I wouldn’t depend on just one set of books to get all of the vocabulary and Kanji.

I especially recommend the Sou Matome grammar books. They have well-translated English (Korean and Chinese, too, I believe) sentences, which are very helpful in capturing the subtle differences in, what often appear to be, very similar grammar. Yes, N1 and N2 studiers will be amazed at how many variations there are on, “Not only is he [good at Chinese], but he is also [good at German]!” or “That’s a mistake [a high school student] might make, but certainly not [a professor].