Read a textbook. Either Genki or if you want to get right in on the action, Sakubi (up to lesson 23)
At the same time as reading a textbook
Binge a premade deck (either kaishi 1.5k or 1k cards of core 2.3k)
Either at the same time as reading a textbook and doing anki or after (I'd recommend after)
Immerse in content like anime, YouTube, Light Novels, etc.
Once you've gained enough input:
Output by typing/writing. If you wanna learn how to write, you can learn how to write kanji through RTK, but you'd already either be doing that prior to the input stage or you'd learn how to read kanji by reading words. You can get somebody to correct you, i.e natives on places like hellotalk or on discord.
You can also study pitch accent and shadowing at this stage. Use kotu.io and achieve 100% on the minimals pairs tests then start listening while outputting.
If you wanna speak to others verbally, get a tutor or somebody to correct you while speaking and start speaking to them. It's fine if you make mistakes, because if you're getting input, you'll be self-correcting anyways. If you output enough, it will sound fluid eventually.
reading and listening how-to:
How to read: get a sentence, search up all words and grammar, try and understand the sentence, move on if understood. If not, take 1-2 minutes to figure it out and move on if you still don't.
how to listen: listen out and try to understand as much as you can. If you can't understand sentences, look out for words. If you can't understand words, hear out for sounds. Once you can hear sounds, move onto listening out for words, then sentences, then entire sections of videos, etc. Search up words occasionally by transcribing into a dictionary by ear.
EDIT: Output section added
by Blinded_Banker