You probably know this, but anyways:

- Lots of reading, both extensive and intensive. Find sources of comprehensible input: sentences that you understand 60-80%, and will help you infer the rest by context. You will need lots of these. For instance twitter accounts in Korean, newspapers, etc.

- Watch shows with subs in your L1, or watch them 2 times: first time in L1, right after in L2.

- Use spaced repetition, but creating your on cards (active study vs passive study). Sentences better than words, bring context.

- Do some writing. Perhaps a journal, or something about your job / field of expertise. Notice the gaps (things you want to say but don't know how). Get it reviewed by a native.

- Have regular 1:1 sessions with a tutor / teacher, eg. on Italki.

If it is important to you, it is worth to spend a some money on it IMO.

Good luck!

I studied Mandarin for a few years back in my home country. I've noticed that despite spending a significant amount of my time studying it was hard to see any improvements. That changed when I first went to Taiwan and stayed there for a few months. My rule was to never use English when I was outside. Even when Taiwanese people would speak English to me (which happens quite often if you're a white person in Asia) I would reply "Sorry, no English" and use my broken Mandarin. I progressed very quickly and gained a lot of confidence to the point that speaking Chinese became a norm.

What I am trying to say that if you are very serious about learning Korean you should research opportunities that will allow you to spend some time in Korea. It all depends on your current position/finances, but it may be easier than you think. There are many scholarships offered to language students that basically cover most of your living expenses. I encourage you to check them out. During my time as a student in Taiwan I've met people of all different backgrounds. Students, senior managers, people with Taiwanese SOs, etc. If you can only do it for a month -- do it. I think going to the country that speaks the language you're learning is the only way to actually improve.

I haven't personally used LingQ, but it seems to be the best way to pick up new languages. It provides a feed of news in other languages with a neat vocab tracker! I haven't learned a language with it yet, but I'm very interested. There's also an excellent interview with LingQ's creator.

---

[1] https://www.lingq.com/en/

[2] https://www.youtube.com/watch?v=TKg23ZFURX0

I haven't tried this but I've heard good things about the Middlebury immersion programs: https://www.middlebury.edu/language-schools/

Seek actual conversations.

Maybe Korean Associations, travel, find an online chat buddy you can facetime if nobody locally.

Weird side story, when I lived in Mongolia many people would pay me not to learn English but just to have a conversation with a native english speaker. They were motivated to not just learn but also to get better.

Change all of your YouTube content to Korean.