I personally use the げんき textbook series for grammar and speaking practice. For kanji, I'm currently working my way through James Heisig's Remembering the Kanji book. Hiragana and katakana can easily be learned online using something like readthekanji.com, or an app or some other resource. My go-to Japanese learning website is Japanese Level Up (jalup.com), and I find it to be super motivating. Using a spaced repetition flashcard app like Anki to learn vocabulary and kanji is also a super effective method for quickly improving your Japanese. Hope this helped! If you have any questions, feel free to ask~