There is no one magic solution. Every person I know who has learned a language to an advanced degree has used a variety of methods, diligently, over a long period of time, depending on their current needs. I can give a brief overview of some tools that I find to be efficient in terms of time and payoff, in no particular order.
1. SRS - Spaced Repetition Software, for flashcards. Anki is the gold standard. It's open source and free on every pc/android/etc except iphone where it's $20 I think. I recommend finding a good starting deck with about 3k to 6k words to help build your core vocabulary. In my case it was "Evita's 5k Korean". For about 6-8 months I grinded 20 new words per day, which means about 30-50 minutes of Anki depending on if you missed a day or not and thus had a backlog. If you have less time I recommend 5 or 10 new words per day.
2. Find trusted resources for grammar and structured learning. You might have to hunt around but for Korean, I found some excellent websites, Youtubers, and textbooks like Korean Grammar in Use I-III. These materials really are the core of your studying. Vocab doesn't help much if you don't know grammar and you certainly can't say anything without vocab. These are how you get to output, i.e. writing and speaking correctly.
3. Find graded readers if possible. Roughly, these are texts designed around 90% comprehension which is a sweetspot for learning new words naturally through context. Unfortunately at the time I couldnt find any for Korean, but I've watched friends use them for e.g. Mandarin Chinese and learn quite a lot of vocabulary in a short time.
4. Find someone who can correct your writing in some form. Whether that's a private tutor or a friend who's native language is your target language and their target language is your native language. In the past I found some dedicated learners through HelloTalk who would trade journal entries with me. I would correct their English and they would correct my Korean. It goes without saying that you need to practice output in your target language when possible, both in writing and in speech.
5. Find a good language exchange and/or friends who speak your target language. By good, I mean a structured language exchange that enforces pairings and language usage. In Seoul I find that most "language exchanges" are excuses to drink and and chat, mostly in English. There was one language exchange that 1:1 Korean language-only pairings for 1 hour, then I repaid that with 2-3 30minute pairings of 2-3 people in English. This is where you put your textbook/solo studies to practice by actually speaking (and hopefully getting corrections). Eventually I hit a plateau and got tired of having similar conversations, plus paying $10 per event. I also found a few lifelong friends who are studying English and thus we can ping each other for random questions.
6. Find some spaces or groups that are -only- in your target language. With the internet it's easier than ever now with Discord. For example, my friend learned a lot of French by hanging out in French speaking gaming servers on discord. There are also apps like Hilokal and HelloTalk, but I haven't used them in a while so I can't speak to their quality anymore. Lastly there are offline options depending on your area. In the US I used Meetup to find language groups and in Korea I use, well, a korean equivalent to find groups in niches I enjoy.
7. Lastly, and this isn't a tool, but "If you want to improve, be content to be thought foolish and stupid." - Epictetus. In learning a language, you will make mistakes and you will say things that sound stupid. It's okay. It's unavoidable and you make good progress by learning from these mistakes, so long as you reflect on them and understand why the mistake occurred. The people who focus on being perfect and making zero mistakes in learning a language, in my experience, do not go very far.
These are some great tips. Having consistent daily exposure to your target language I think is important. Compelling graded readers can make spending that time every day enjoyable and not feel like a chore. A stress-free positive learning environment helps quite a bit with the subconscious process of language acquisition; it's what Krashen calls the "Affective Filter Hypothesis".
1. SRS - Spaced Repetition Software, for flashcards. Anki is the gold standard. It's open source and free on every pc/android/etc except iphone where it's $20 I think. I recommend finding a good starting deck with about 3k to 6k words to help build your core vocabulary. In my case it was "Evita's 5k Korean". For about 6-8 months I grinded 20 new words per day, which means about 30-50 minutes of Anki depending on if you missed a day or not and thus had a backlog. If you have less time I recommend 5 or 10 new words per day.
2. Find trusted resources for grammar and structured learning. You might have to hunt around but for Korean, I found some excellent websites, Youtubers, and textbooks like Korean Grammar in Use I-III. These materials really are the core of your studying. Vocab doesn't help much if you don't know grammar and you certainly can't say anything without vocab. These are how you get to output, i.e. writing and speaking correctly.
3. Find graded readers if possible. Roughly, these are texts designed around 90% comprehension which is a sweetspot for learning new words naturally through context. Unfortunately at the time I couldnt find any for Korean, but I've watched friends use them for e.g. Mandarin Chinese and learn quite a lot of vocabulary in a short time.
4. Find someone who can correct your writing in some form. Whether that's a private tutor or a friend who's native language is your target language and their target language is your native language. In the past I found some dedicated learners through HelloTalk who would trade journal entries with me. I would correct their English and they would correct my Korean. It goes without saying that you need to practice output in your target language when possible, both in writing and in speech.
5. Find a good language exchange and/or friends who speak your target language. By good, I mean a structured language exchange that enforces pairings and language usage. In Seoul I find that most "language exchanges" are excuses to drink and and chat, mostly in English. There was one language exchange that 1:1 Korean language-only pairings for 1 hour, then I repaid that with 2-3 30minute pairings of 2-3 people in English. This is where you put your textbook/solo studies to practice by actually speaking (and hopefully getting corrections). Eventually I hit a plateau and got tired of having similar conversations, plus paying $10 per event. I also found a few lifelong friends who are studying English and thus we can ping each other for random questions.
6. Find some spaces or groups that are -only- in your target language. With the internet it's easier than ever now with Discord. For example, my friend learned a lot of French by hanging out in French speaking gaming servers on discord. There are also apps like Hilokal and HelloTalk, but I haven't used them in a while so I can't speak to their quality anymore. Lastly there are offline options depending on your area. In the US I used Meetup to find language groups and in Korea I use, well, a korean equivalent to find groups in niches I enjoy.
7. Lastly, and this isn't a tool, but "If you want to improve, be content to be thought foolish and stupid." - Epictetus. In learning a language, you will make mistakes and you will say things that sound stupid. It's okay. It's unavoidable and you make good progress by learning from these mistakes, so long as you reflect on them and understand why the mistake occurred. The people who focus on being perfect and making zero mistakes in learning a language, in my experience, do not go very far.