The simplest way is to sign up for in-person lessons, do your homework and keep attending until you are fluent.
In addition or even as an alternative, there are a few things you can study on your own:
1. Phonology. Learn the International Phonetic Alphabet and use it to understand how the pronunciation of your target language differs from your mother tongue. I like using Wikipedia's help pages of the form https://en.wikipedia.org/wiki/Help:IPA/Any_Language for that.
2. Vocabulary. In the beginning, it's probably most efficient to learn new words ordered by decreasing frequency. Once you can read simple texts with the help of a dictionary, learn words you had to look up repeatedly.
3. Practice. Use a spaced repetition program like Anki ( https://apps.ankiweb.net/ ) and make your own flashcards. Pre-made decks are unlikely to take you in exactly the direction you want to go.
3. Listening. Even before you're able to understand anything, you can get a feeling for the language by watching subtitled shows. ( https://www.viki.com/ has a decent selection in East Asian languages.) Later you can turn off subtitles (or switch them to the target language) to avoid overly relying on them.
4. Reading. Find something you can enjoy and read a little of it every day. In the beginning, that might just be a single sentence; you'll naturally end up reading more as your skill improves.
5. Speaking. This is the hardest to do on your own, and you definitely need a solid base vocabulary before you can have an intelligent conversation. To speed up the process, you can try finding a partner who'll be willing to listen to you babbling as long as you do the same for them. You need to make sure not to fall back to your mother tongue too easily, though.
6. Form a habit. If you have some fixed amount of time dedicated to learning every day, you're not as likely to procrastinate on it.
I'm an ESL. I started learning English at school, then I started reading English novels (I remember reading the last Harry Potter book a few months before it was translated). And then a lot of time spent on the English-speaking parts of Internet.
In addition or even as an alternative, there are a few things you can study on your own:
1. Phonology. Learn the International Phonetic Alphabet and use it to understand how the pronunciation of your target language differs from your mother tongue. I like using Wikipedia's help pages of the form https://en.wikipedia.org/wiki/Help:IPA/Any_Language for that.
2. Vocabulary. In the beginning, it's probably most efficient to learn new words ordered by decreasing frequency. Once you can read simple texts with the help of a dictionary, learn words you had to look up repeatedly.
3. Practice. Use a spaced repetition program like Anki ( https://apps.ankiweb.net/ ) and make your own flashcards. Pre-made decks are unlikely to take you in exactly the direction you want to go.
3. Listening. Even before you're able to understand anything, you can get a feeling for the language by watching subtitled shows. ( https://www.viki.com/ has a decent selection in East Asian languages.) Later you can turn off subtitles (or switch them to the target language) to avoid overly relying on them.
4. Reading. Find something you can enjoy and read a little of it every day. In the beginning, that might just be a single sentence; you'll naturally end up reading more as your skill improves.
5. Speaking. This is the hardest to do on your own, and you definitely need a solid base vocabulary before you can have an intelligent conversation. To speed up the process, you can try finding a partner who'll be willing to listen to you babbling as long as you do the same for them. You need to make sure not to fall back to your mother tongue too easily, though.
6. Form a habit. If you have some fixed amount of time dedicated to learning every day, you're not as likely to procrastinate on it.