I think as with any language you just need to practice a lot and get used to talking in that particula language.
I don't think there's really any other method than listening to people talk in that language and then talk yourself.
You may also need some talent though but that I'm not sure about. I used to get good grades because I have a "soft accent" so I could with no trouble adjust to a different accent. That helped when I had no clue haha. It seemed like I'm actually fluent. For example, one time in German class my teacher said that I have a beautiful soft accent and that's why I got a good grade...even though I knew less than anyone else in class