I took Japanese for four years in high school and I think I’m alright at it ig. Yeah for kana you just straight up memorize it however you can, it’s basically equivalent to the alphabet, no excuses or bs. You should not be getting stuck on this step.
For grammar, like kev said, there’s a bunch of resources out there that will straight up tell you how all the common structures work, but I’d also add that putting an effort into learning the ins and outs of each particle will really help with your general understanding of grammar.
Vocab is something that I never really bothered to grind because I didn’t feel the need to, so I’ll defer to others on this, but I personally never found flashcards and the like very engaging. Obviously it’s important to build up a base vocab before you can start to learn by consuming content, so you should look into basic vocab list for stuff like this/that, food/drink, etc. Beyond that, I think it’s way better to read level-appropriate material and learning words as they show up. But again, it really depends on the type of learner you are.
Extra-ish thing I like to do:
Sometimes I just pick a random webnovel on https://syosetu.com/ and translate the first chap for funsies. It’s kinda funny how whack some of the plots are.