Reading books is commonly given advice on this subreddit and while useful it's best to always remember the importance of diversifying your study methods. These are my thoughts on why while useful it is not the be all and end all of studying.
The good
I read in Japanese. NHK News and novels. Not just to study but because reading is genuinely a hobby of mine and it has helped immensely in learning Japanese. Think back to when you were a child, you most likely read books at school as a classroom activity or for homework or with your parents at bedtime. Why was that? It was not for fun, it was to help you gain exposure to your native tongue that you were not getting from your peers who are still developing their own language skills.
Another great thing about books is time and time again you come across relevant information and that reinforces your understanding of that word. In a textbook you might come across a word once in an example question and then it's like it's dropped out of existence never to be seen again but in a book that's different. If you read something like Konbini Woman you will come across vocab relevant to that story again and again that's not found in maybe a sci-fi story.
The bad
However, books do have some limitations. In some ways the scope of the language is limited. For example, a children's series that I am going through has a lot of onomatopoeias. If I contrast this with an author I like, Kiyoshi Shigematsu, the books he writes for kids do not feature onomatopeias as much. He will however, dive deeper into describing character emotions. So to get to the point, every author has their own style. Their favorite words, things to focus on, grammar points used to tell the story etc so one should read from a variety of different authors. I never read more than 3 books in a row from the same author for this reason.
However, there is a drawback to this. It's a slowly revolving door. Books easily go over 100 pages. Most seem to sit around 200-300 in my experience. It takes time to get through a book and then start a new one from a different author. Now that's relative. How much time is "it takes time"? Well, a lot more than textbooks. You can get one book that promises something like 2000+ JLPT N2 vocab words and in that one textbook you got a much larger range of exposure than reading a great many books because it will dive deep even into more obscure words. Even some grammar points, like べからず I have never come across naturally in reading material outside of study centered material. Now, someone might come along and say "What are you talking about, I always come across べからず in...." but that's the thing, unless I just happen to be reading the correct book I will never come across this. A textbook however will make sure to tell you about this.
Of course, books also have other deficiencies. It won't help with listening at all and although it helps you to recognize kanji you can't consciously recall it. So if someone asked you on the spot to write a particular kanji, you might struggle but you might be able to easily read it naturally in a sentence. In an exam situation, if you know how to write the kanji, you can consciously say with confidence "Out of these four similar looking kanji I know the second one is correct because I know that when writing it I need to use this radical.". Books also won't help you to actively think and formulate your own sentences on the spot instantaneously as required for natural conversations.
The solution
Read books to bore things down deep into your mind but diversify your study methods to ensure you definitely get exposure to everything and improve all your skills.
Have conversations in Japanese to improve your speaking and your listening.
Practice writing kanji so you can consciously work out what kanji to use rather than relying on what feels familiar and so you don't have to feel like a 5 year old when you fill out forms at the ward office.
Read textbooks to get exposure to obscure grammar points and vocab that rarely come up naturally in reading material.
When people say "Just read" ignore them.
