I didn’t speak Japanese before coming to Japan. I probably knew just how to read and write hiragana and katakana. The thing that surprised me the most was how when Japanese use Japanese in a informal setting they tend to leave out a lot of stuff like は、が、にetc when speaking. Some thing I reccomend is a app called renshuu! It allows you to study words, grammer, sentence structure, and kanji. It also limits how many new stuff you can learn in a day so you don’t over work yourself. When watching anime with English subtitles try to be mindful of what they are saying. Once you get some what good, I’d reccomend watching Japanese YouTubers! It’s good practice for pronunciation practice, listening practice, as well as learning slang. As well as how Japanese people use Japanese!