I'll just copypaste my usual guide:
"First, I recommend you read this : http://guidetojapanese.org/learn/
It will give you the essentials and it's always a good place to refer yourself to when in doubt. Or when you want to understand some new gramamtical concept.
Also read this : https://8020japanese.com/japanese-sentence-structure/
It's a really great explanation of the fundamental principle of japanese language.
This at least should give you an idea of how the language is. For serious learning, I use two things...https://wanikani.com
This here is a web app that aims to teach you the necessary kanji in life and a lot of vocabulary. It's immense work (been doing it for 2 years and only now reaching the end) but it's a necessity if you want to learn to read.
Finally, this : https://bunpro.jp
It's the same principle as above, except focused on grammatical points. It's going to make you progress much faster than wanikani, but doesn't teach vocab. Still, it will allow you to understand correctly the sentences you know the words of."
There you go, this is all what brought me here.
Also I recommend these bad boys : https://www.amazon.com/Japanese-Cheat-Sheet-Pack-Nihonshock-com/dp/0988660512
It's an amazingly concise and well organized summary of many essential grammar points as well as "spoken" japanese, slangy expressions, common traps etc. I have them pinned around my room and they're invaluable for when I need to remember something real quick to express myself in japanese.