You can just force yourself to learn the language by changing the language while your gaming or the language on your phone for example. At first it'll be really tough but after a while you'll get the hang of it.
The most effective way however probably is just living in a foreign country for some months to learn the language. Nothing helps better than forced communication for a while. (You will have to want to learn it of course and not just approach everyone in english.)
Great suggestion! And that's super true about being in another country and avoiding the familiar language. It's so easy to default to what you know really well, but that's obviously not going to help. What language did you learn by doing these things? :)