learning the kana is really easy, it can be done in a day if you work hard enough. my suggestion is to the hiragana/katakana symbol like 30 or so times and also write the sound it makes. make sure to read various texts - ensure that the kanji has furigana to begin with. read them out loud as well so you get a feeling for how to pronounce the characters as most of them are a lot further from English or the romaji as you think they are (ら(ra) - a mix of L and R, ふ(fu) - a mix of F and H). i personally recommend this website - https://www.wasabi-jpn.com/japanese-lessons/fairy-tales-and-short-stories-with-easy-japanese/
there are a few hiragana that look very similar, れ、ね、わ。な、た。ぬ、め、あ。etc etc. if you feel the need to learn the difference, you can write them down next to each other and take your time learning the different strokes.
the most important part of retaining what youve learnt is putting it to use. make sure to consistently read and write in japanese (you can find manga on the site i recommended). write your friends names in katakana for them, write sentences in katakana, learn japanese ONLY using the 2 kanas - thats very important. eventually you wont need consistent practice and it will come very easily, katakana will be the hardest to retain.
as for kanji, its hard, theres no getting around that. keep reading and reading and reading, learn the strokes (or just general strokes), write it down, learn both the kunyomi and onyomi readings, learn to use it in a sentence, the variations of it etc etc. make sure you learn a few each day or week sarting with the most important ones like 私、木、土、木、金、火、日、月 etc etc.
have fun!!! if you have anymore questions feel free to message me
I'm planning to visit Japan within the next five years, and I want to learn Japanese in the meantime so I don't look and feel like a complete idiot there. But my biggest problem is learning and retaining the Japanese alphabet. For those of you familiar enough with the language, how did you manage it?