Best resources/way to learn Japenese?

I'm currently a high school student, planning to go to college in Japan, and continue to live there for the rest of my life. I've heard that I should learn as much as I can before then, and I was wondering if anyone could help with that? (I don't mean teach me I mean help me figure out where to get started.) Any links to online courses (preferably not anything too expensive), a textbook you think everyone should begin with, a website you can start at any level on, a workbook with the proper way to write in Japanese. I've also heard you should refrain from learning romaji, so maybe something without that. Anything would be a great help, but I'm also trying to learn this on my own, so hopefully something more suited for that. Thank you!

Tae Kim's guide is a free online grammar course. It is an acquired taste, but fairly complete for a beginner course. Anki is a free flashcard app for your computer, you can use it with downloadable shared decks of cards to memorise vocabulary (Core 10k is a good deck). YouTube is now an excellent resource. Channels such as 日本語の森 and Japanese Ammo with Misa are recommended. HelloTalk is a free app for your phone which can connect you to Japanese people for language exchange.

Hope this helps.

Regarding text books for learning kanji, I would suggest the ones using Heisig’s method. It is a systematic study method aimed at people who want to learn all kanji in a systematic and easy to remember way, rather than learning them as Japanese children learn them by occurrence.

I also used Skritter for learning how to write, but it isn’t free.

Personally I am not a fan of online courses. Maybe there is some local school in your region that offers courses? With Japanese it is relatively easy to find beginner courses, while more advanced courses thin out quickly.

I can only advice you to start Kanji as soon as possible. I always skipped it (and still passed JLPT N2 somehow) but knowing Kanji makes everything so much easier.

Wanikani is a great resource for studying Kanji (though for a student the price might be quite steep)
The SRS method gives you the study plan and you don't have to plan on your own which Kanji to review when and it also makes it a bit of a game.
I guess there is some sience behind it all, but I just really like it because I don't have to open a book and I have "someone" controlling me. I can't just say I know that Kanji I skip it today, which I sometimes did with books.

and i can advice you to get used to the language. TV, Radio, Podcasts, Books and so on. just as much exposure as possible.

Japan Foundation offers a lot of free online Japanese learning resources. And they have branches in many countries in the world:

https://www.jpf.go.jp/e/about/index.html

I really like the Japan Foundation London UK website the best for language resources, and I can use it even though it isn't my home country - here is a link:

https://www.jpf.org.uk/language/teaching_resources.php

Have fun with your studies!

Thanks for answers! it's useful for me too.