So this isn't anything extraordinary but it's been helping me to improve my Japanese a lot.
I've been reading daily. One of the best sources I can recommend is tadoku readers, but NHK Easy News works well, or any other story or media you can find that you feel comfortable with. My ritual with Tadoku readers is to read through the entire story, writing down a translation for it in a notebook. I look up words as I read that I don't know as well as grammar points. Once I've read through it a single time and translated it, I go through a second time and write down a vocabulary list. Every word I didn't know, I write down (the kanji, the reading and the definition). I also make a grammar list, taking note of any grammar I didn't know or struggled with. I write down the use case and the sentence from the book. Then I move onto the next book and do the same.
After I've worked through a few books, I go back to an older book that I read awhile back and see if I can read through it without needing to look anything up.
Of course, I also do wanikani on the side and practice making sentences with the words and grammar I've learned.
This has helped a lot more than just drilling grammar books. Seeing things in "the wild" and in context helps a lot and when you keep running into the same structure or vocabulary several times, it really helps it to stick.
Again, nothing too out of the box here but sometimes we overlook the simple things. If this helps even one person, I'd be happy.
My next plan is to start reading manga and then watch the corresponding anime, and read novels. But in my opinion, if you want to get better: Read, read, read. Read as much as you can. Once you're very comfortable with reading, move on to listening. Then speaking. You can ofc do a little of everything (and should) but focusing mostly on reading then listening then speaking I think has a lot of merits. Feel free to disagree though but whatever you do, reading helps a lot.
by viptenchou