As I close in on two years since I started learning Japanese I can fairly say I've experimented with just about every tool (both tech and mental) out there and figured it would be nice to consolidate the big hitters into one place. I'm by no means fluent, but I am able to read just about anything I encounter (barring some dictionary lookups) without thinking much of grammar or sentence structure. Things just make sense, similar to how English feels when reading. There is no intentional translation, the words simply enter my brain, are processed, and meaning is extracted.
Before I begin to discuss my thoughts, I should mention my focus was on immersion, not using text books. This means a typical "study" session just consists of reading books, Wikipedia articles, blog posts, or enjoying a good show (if you are interested in following a similar approach I highly recomend reading TheMoeWay). I use a spaced repition flashcard program called Anki, but never has it been my only resource. Flash cards and proper studying (e.g. memorizing grammar & vocab) are meerly supplements to speed things up, but not by any means necessary.
Now that thats out of the way, what tools have proved critical but are not exactly common knowledge?
My largest gains have come from getting myself an android ereader. You can find some models for around $250 USD. I personally use the Boox Go 7 BW and really enjoy it. Some may ask "Why not just get a kindle?", well, if you value owning your books, avoiding propritery software when possible, and not having ads shoved into your face, perhaps it's time to take a step back. Now, I will not say Boox is perfect. It's far from. They have a reputation for bad customer service, buggy screens, and broken firmware updates (as a screen bug I was having only occured on a more recent firmware version). But, if you can tolerate the rough edges, the screen is very responsive and crisp, devices are nice and light, excellent battery life, you get access to the android app store, and (at least the model I mentioned previously) won't break the bank. At the end of the day, I am just a dude on the web, so please don't listen to me blindly - do your own research first!
Now, why have I found an ereader to be so ground breaking? Well, besides the fact my eyes no longer feel they are falling out of my face after a long reading session on the computer, I have been able to get Anki and AnkiConnect Android setup, allowing me to mine vocabulary fully from a tablet without any internet connection. The screen is fast enough to where mining new words is quick and painless and getting Yomitan setup (a popup dictionary browser extension) was straight forward. I now have a device I can take anywhere, mine new words, and lookup unknown ones with ease! It's quite effective at salvaging dead time through banging out a few pages or reading an interesting blog post.
A trend among the hardcore Japanese learning communities is spending absurd hours immersing, cutting out social life, and removing any form of media not in the target language. While I do agree removing media that is not in your target language is good, obsession in this case is not. You need to be okay with taking some time away from your immersion to go socialize, watch a movie in your native language with friends, or hell, even have a day where you don't immerse at all.
You need to remember, learning a new language is pointless. Unless you are being forced, it will likely not cause substantial improvements to your life and your day-to-day won't be a whole lot different. You are going to devote thousands of hours, buring a signifigant portion of your life candle, to learn this language. So, it's important to ask internally why you want to learn a new language in the first place. I don't have a very good answer, but I found peace in realizing I would spend these hours consuming English media already, so why not just make it Japanese? I'll get to enjoy a good story and accidentally learn a new language, which is pretty killer.
In many cases, learning a new language can feel quite similar to getting good at a very hard video game. It takes huge amounts of time, at the start you are clueless, and there are many skills to be leveled up. I think the translation is closest to playing an RPG where you are able to tackle harder books/shows as you level up. The linear progression in difficulty for reading may look something like childrens books → young adult books → novels → academic papers (or generally works targeted at educated adults). As more time is spent at a specific level, the next gradually becomes easier. I started reading Japanese with childrens(ish) books (e.g. よつばと！ & また、同じ夢を見ていた) and now am able to read 村上 春樹, so I would say I am comfortably able to read novels targeted at adults!
Many folks take advantage of humans reward system by logging hours and segregating based on categories (reading, listening, speaking) to help visualize progress. I've even seen people go so far as to do some google sheets programming to literally have a level associated with their skills that increases as time spent in each category does (which is pretty damn neat). I will say though, please be careful to not obsess over numbers. Just as proper study is supplementary, so is tracking immersion hours. When I first tried to learn Japanese in 2021, after a few hundred hours of immersion I found myself so obsessed over how much time I spend immersing that I couldn't actually get myself to immerse! It's almost paradoxical how obsession over time in the short term will lead to less time in the long run. It's very easy to dig yourself deep into this hole and as you will have days with little immersion, see there is no leveling up happening, get down on yourself, and repeat. I personally do not log my hours anymore due to my past experiences, but others have had great sucesses with this approach, so just use your head and observe your emotions.
This advice deviated from my orignal intention of talking about the actual technology I have found useful, but I think this is more helpful. So, please listen to your mind, take care of yourself, exercise regularly, socialize, and enjoy learning a new language! It's an incredibly rewarding process and a very fun journey, and I hope my words are of some value.