I'm fluent in German, English. I'm living in Japan and am almost fluent in Japanese and quarter fluent in Korean. I also recently started Hungarian and Spanish.
The most important part in my opinion is to live in a country that speaks the language you want to learn. You have to immerse yourself as much as possible with the culture and language.
Also very important that you aren't afraid to try to use what you learned. Even though it's very basic, you learn a lot by actively trying to understand and use the language. It might be tiresome and frustrating at first, but you will learn crazy fast. What I mean with that is: Change your OS to that language and accept that you don't understand anything at first.
Make internet friends and refuse to use English with them even though you have to translate every second sentence. Every time you see something you don't know, try to understand why it's written that way.
Lastly, if you have time and money: Do a 6 months ~ 1 year intensive every-day language course in the country that speaks the language you want. By doing that every day AND surrounding yourself with the culture + language, you will be able to speak after 6 month and become very good with it after 1 year.
On languages from a similar family (speak: English <-> German <-> French <-> Spanish || Japanese <-> Korean), you can get pretty far by buying books or doing internet courses.
For words, I prefer the spaced repetition method of tools like Anki. Important here is that you only create flashcards for words that you personally encountered to allow your brain to make connections to where you saw that word. Don't learn from wordlists.
The most important part in my opinion is to live in a country that speaks the language you want to learn. You have to immerse yourself as much as possible with the culture and language.
Also very important that you aren't afraid to try to use what you learned. Even though it's very basic, you learn a lot by actively trying to understand and use the language. It might be tiresome and frustrating at first, but you will learn crazy fast. What I mean with that is: Change your OS to that language and accept that you don't understand anything at first. Make internet friends and refuse to use English with them even though you have to translate every second sentence. Every time you see something you don't know, try to understand why it's written that way.
Lastly, if you have time and money: Do a 6 months ~ 1 year intensive every-day language course in the country that speaks the language you want. By doing that every day AND surrounding yourself with the culture + language, you will be able to speak after 6 month and become very good with it after 1 year.
On languages from a similar family (speak: English <-> German <-> French <-> Spanish || Japanese <-> Korean), you can get pretty far by buying books or doing internet courses.
For words, I prefer the spaced repetition method of tools like Anki. Important here is that you only create flashcards for words that you personally encountered to allow your brain to make connections to where you saw that word. Don't learn from wordlists.