Answers will naturally vary on this topic as there is no definite "this way is the only/best way to do it" approach and everyone will need to experiment a bit to figure out what works best for them.
With that out of the way, below my suggestions based on a mix of how I learned the language this far and what I learned about learning this language during this time:
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1) Learn reading Hiragana, Katakana, and Kanji, in that order, ASAP.
I cannot stress this one enough. If you haven't done so get Hiragana and Katakana out of the way ASAP, but do not wait to long with learning Kanjis. I studied Japanese for quite a while (3 years?) mostly focused on text books getting some grammar/vocab etc. in place with only dabbling in Kanji on the side. I was not really feeling as if I was making any progress during that time.
I then discovered WaniKani* by chance and that was just the right tool for me at the right time. I ended up learning most of the important 2000 Kanji each adult needs to know within slightly over a year (plus another 6000 vocab items that WaniKani teaches you on the side to drill in those Kanji readings). The effect of this focused Kanji learning was noticeable during the first 3 months already were I suddenly was able to start understanding more and more pieces of a sentence and my struggles in understanding content more and more shifted from "what is this squiggly thing?"-lookups to "what is the grammar behind this?"-puzzlement. This was a huge motivational boost and I am still quite amazed from time to time how effortless reading is now and how much I can now understand from just glancing over sentences, even if I do not truly understand the fine nuances of the grammar involved.
Learning to read is of utmost importance as it has multiple benefits going for it: It opens up a lot of material to you, you automatically learn vocab on the side [as the best way I found to learn a Kanji is to also learn relevant and common vocab associated with it], and it frees up a good chunk of your precious study time to focus on other things than looking up Kanji/vocab all the time.
*Disclaimer/More deliberation from my side: I only found renshuu after I was 60% through with WaniKani. I do not know how Kanji learning with renshuu really is, but if you want you can try using renshuu coupled with the WaniKani Kanji and Vocab lessons found in the study library to get the benefit of having the Kanjis paired with associated vocab and the "building block" experience of higher level vocab using a mix of various lower level Kanji. This does not emulate the whole WaniKani experience, as WaniKani itself was based on teaching you (WaniKani defined) radicals first and then build mnemonics out of those "radicals" for the Kanjis that are constructed out of them. I am not really a mnemonic type of learner so for me that benefit was minimal (but the structure and SRS was what lead to me sticking to it).
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2) Consider taking a real course for a while
This can be difficult, depending on where you live and what your financial situation is etc. If possible, it would not hurt especially in the beginning to get a real teacher-led course for a while. Benefits I see from this would be: You get some pronounciation practices, you will definitely learn hiragana/katakana at the start, you are introduced to one of the many textbooks that are out there (get an idea how to work with it by virtue of having a teacher use it), and it brings some structure into your learning.
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3) If taking a real course is not an option due to various reasons, consider to still get a textbook
Textbooks have the benefit of introducing vocab and grammar in a certain context and building up later lessons on what you learned before, giving some much needed structure and guidance on how to approach learning this rather difficult to learn language. There are a myriad of textbooks out there and when you ask 5 people which book you should use you will probably get 6 recommendations out of it.
I personally used JFBP (japanese for busy people), but mostly because this was the textbook that was introduced to me when I took Japanese language courses at the very beginning and thus had it both lying around and was familiar with it. There are a lot of people that will swear on Genki being the best (and others saying the same about Minna no Nihongo). There are also a lot of online/youtube courses, but I have am not really familiar with those
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4) Keep your learning consistent / get a daily routine
It is better to have a constant habit of "small doses" of Japanese every day than having irregular bursts of Japanese learning/exposure distributed over the week. Having a good SRS (like Renshuu! (^-^)b) helps a lot in managing this here, provided:
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5) Don't overwhelm yourself
You are in for this for the long run. You have to figure out what your acceptable level of daily Japanese routine is, but be aware that if you push too many new terms in every day your daily reviews will steadily increase. If left unchecked this will both eat away all your Japanese study time (by you ending up spending hours just to review vocab/kanji) and might end up burning you out. While the SRS helps in spacing reviews, do not underestimate the effect later reviews of higher level items can have on your daily review queue [especially if you start making mistakes, which are natural to happen].
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6) Immersion!
It is difficult to say when the best time would be to really start diving into this, but only doing reviews all day won't really teach you the language either. Immersion is important to provide much needed context to what you learn and help in determining which vocab/grammar points are truly important vs. those that are just obscure seldomly used items. Immersion does not mean "go live in Japan for 20 years" (but you can do that if you like!), but rather trying to get more and more Japanese stuff into your day, be it some reading, some youtube/movies, some podcasts, or "just" thinking in Japanese sentence fragments. Use the language! Ideally with something that you really like doing (like to play video games? nowadays you can just play a lot of Steam/GOG games in Japanese, provided you know enough to actually understand them and not have to look-up everything). Important for this immersion bit is to not to try to understand everything to 100% and certainly not go crazy and add every unknown vocab to your renshuu schedules (too many new reviews eating up more of your precious immersion time). Rather pick a handful of words you believe are a must-have for you and move on to other materials. Moving on will also help in seeing what are really just one-off "odd" vocab you have to focus on if you really want to know them by heart and what are very common vocab you will encounter everywhere which you thus will recall in your sleep without ever having them added to any of your schedules.
It is certainly easier to immerse yourself the more you know (i.e. can read a larger amount of Kanji's (1000+?), have a lot of vocab under your belt (4000+?), and know some basic to intermediate grammer (up to N4?)), but depending on the materials you are looking at very little knowledge might be needed.
If others do not do it before me, I can maybe later go through my bookmarks etc. for various reading materials and the like.
