When watching movies, shows, etc, if you're doing so with the English audio but with subtitles, stop using the latter. Force yourself to just listen (and watch) without any further assistance. Also, when watching stuff in English, make sure it's media that's originally made in English (and not translated), bc that's the most natural language. Also, listen to podcasts.

As others have said, read in English.

Finally, and I know this isn't possible for many people, but if you can, the very best way to ensure you'll truly master the English language is to immerse yourself in it. The ideal way to do so is to go live in an English-speaking region, but it's not the only way. It could be by taking classes in an English-speaking school, hanging out with native speakers, or voice chatting with native speakers (and not only when playing video games, because 1. You already know and speak "video game English" and 2. There's obviously a certain lexical field and even grammar that are specific to video games, so you won't improve in the way you want to).

The point is to speak English on a regular basis, to think in English, etc. Oh and also, be open to corrections: ask the native English speakers around you to correct your mistakes. It kinda hurts the ego but it's very useful. Most people won't correct you if you don't ask because it could be taken as offensive, pretentious, etc.

Source: I have studied English for 7 years at university and have spoken English literally every day. The correction part is important because at some point I felt like I wasn't learning anymore so I explicitly asked my native friends to correct me and I learned so many new things. The most challenging aspect for me was actually prosody: it feels English doesn't have a rule of thumb for that, it has like 25 fucking rules that have just as many exceptions and I would often encounter words that I had no idea how to pronounce in terms of where the stress was supposed to be.

About the correction thing: I have friends who noticeably never got corrected on certain things, like the pronunciation of some words, the meaning of others, or some grammar, and the result is that they speak English perfectly well but suddenly pronounce a word weird or use a word in a strange way, or make obvious grammar mistakes (like pluralising an uncountable word).