I haven't really tried to learn japanese seriously, but from my own experience learning english, I'd say that the most important thing is immersion. Most non-native fluent english speakers are so out of necessity, often because they are into something without information or a community in their native language. This doesn't apply as well to native english speakers because everything is translated to or written in that language. You should try to correct that: if you want to learn about something regarding anime or related to Japan, try to read pages written in japanese; you could also watch anime with japanese subtitles, and it doesn't hurt to listen to the same piece of media multiple times. At first it will suck since you have to look up everything you don't understand and you might only get the gist of whatever you consumed, but by doing this your comprehension will quickly improve. You're better off trying to make sense of a japanese text than spending literal hours on one Anki deck.
Grammar is the second most important thing. Unless your brain is extremely good at pattern recognition or you spend many years doing 24/7 immersion, you need some knowledge of syntax, whether it is because you want to understand complex structures or because you want to create your own sentences. I've heard good things about
Tae Kim's grammar guide and
Cure Dolly's videos, however, I haven't used these resources myself.
As for vocabulary, the best way to learn terms and words is by natural exposure within the context of a real sentence; that is, if you find an unknown word whose meaning you can't infer, look it up in a dictionary. If you find that word often, it's a good idea to remember it with a Spaced Repetition Software like Anki. Do note that Anki and SRS in general are memorization tools, not learning tools, which means premade decks are usually worthless unless you've already learned the contents of them.
This page and
this article are great introductions to memory and the spaced repetition effect, and if you use Anki, learn
how to use it effectively,
its options,
its plugins,
and what you can do in it. Advice on memory and Anki is often contradictory because everyone is different and has different use cases, so test different settings and use whatever you feel more comfortable with.
And regarding kana and kanji, writing them in a notebook
FIFTY MOTHERFUCKING TIMES kinda helps to build recognition and muscle memory. Of course, you should follow the stroke order (you start seeing patterns even in such a small set like the kana) and you may want to take a look at
how professionals write, after all, you don't learn a new writing system everyday.
Please take this post as a set of suggestions; you should use and do whatever is best for you.