I've been studying intensely for a few years now and have found a single book that never gets "too easy" like Genki 1 and 2 do. Not to mention that a buddy of mine who scored an almost perfect score on his N1 exam told me about this book which is what I've been using ever since:
A Dictionary of Basic Japanese Grammar
This should be more than enough for all the grammar you need on an understanding level. If you want to reach a scholarly level in Japanese, you'd get the Intermediate. But even my friend says that a lot of the grammar on there isn't that common and the ones you'll learn that are on there are better learnt on a case by case basis.
But definitely pick up that one book and know it as well as you know your Hiragana and Katakana and you shouldn't have a problem talking and understanding Japanese.
If you have trouble getting through the book, I recommend going through the Japanese from Zero video series on YouTube at least twice before coming back to this book. That's what I did a few years ago anyway.
After that, you can watch Cure Dolly on YouTube for a more realistic look on Japanese that removes all the fluffy crap that most educational channels have (i.e. making sound arguments on why learning to write Kanji isn't as useful anymore--which after filling up about 500 pages worth of Kanji and being able to literally pull Kanji out my ass, I 100% agree with).
There's going to be a lot of people that will give you advice and most of it is horse shit that comes from guys with barely 3 months into this so you'll have to watch out for those. The top comment is a really good example. There's just so much to learn that it's ridiculous to try to attempt to explain it all and not only that, you have to be pretty fucking arrogant to think that your explanation is better than someone who's co-written Japanese educational books with actual Japanese people (the book I mentioned above).
So watch out for people like these since they're rampant on this sub.
I'd share this one, I really like it.
I usually refer to Dictionary of Basic Japanese Grammar for these. The explanations are more clear and concise to me than resources I’ve found online.
> but I found all the resources it links you to help more than the actual site does!
bunpro is a good site to know what grammar point you can study next, because without a textbook you might end up with something far too advanced. Here you are able to just go through the things sorted after level.
So I follow their lead and when I need more information on one point I look it up in the Dictionary of Basic Japanese Grammar. I usually write down a few things in a notebook and add more explanation into the "add note" part you have above every grammar point on bunpro.
San Diego State University 3rd year Japanese Minor student here (2 years of Japanese in High School on Yokosuka Naval Base, Japan) . Like the others, I would recommend going through a tangible textbook. It'll have a structured compilation of grammar notes, sentence examples, stories in Japanese, useful everyday vocab, and most importantly, cultural points that'll help justify the Japanese thought behind grammar structutes, why some Kanji is drawn a certain way, etc.
One note I want to make is that the problem English-speakers have when learning Japanese is that they think in English, not as a Japanese person. I was once told by my High School teacher that learning a language is learning the culture. Immerse yourself in Japanese thought (i.e. Learn Japanese customs, traditions, habits, and other cultural points), and you'll find that learning Japanese is easier if you orient your mind to think like a Japanese.
My second piece of advice is to absolutely master Hiragana and Katakana writing systems, what each one is used for, and how to write them without thinking. You can't spell words without letters, and its hard to learn vocab if you're focused on how the characters are written. The entirety of the spoken and written language, including all 2000+ everyday Kanji characters, can be broken down fundamentally into those 46-some characters and associated sounds, so mastering those systems to a second nature-degree should be a focus of your studies.
I've had two Japanese professors, both being native Japanese people, that recommended "A Dictionary of Basic Japanese Grammar." I don't have it yet, myself, but from the printouts and clippings that I've seen from the book, it's a really good desktop reference for native speaker-level Japanese grammar. However, I've noticed that the book is mostly useful when you have already formally learned a grammar point and are looking to expand your knowledge base on that grammar point; it's like how you don't learn English by reading a dictionary.
As for online references, I've recently stumbled upon a site known as Tae Kim's Guide to Japanese (below). It's a really good read; he covers important grammar and more, and it's free.
Best of luck in your studies! がんばってください。
A Dictionary of Basic Japanese Grammar https://www.amazon.com/dp/4789004546/ref=cm_sw_r_cp_apa_i_WEmSCbJTQZT0H
Tae Kim's Guide to Japanese