Whenever you got an English fiction or non-fiction, magazine or newspaper or a 2000 page literature, read out loud and record your reading,(with a MP3 player/recorder, it's really simple nowaday) then listen to what you recorded down after a few paragraphs so you know where you need to adjust on words. If you dont know how to pronounce certain word, ask your teacher, or maybe an foreign with English as NATIVE language friend to help you out and have him/her record the pronounciation for you.(some of my friend's whatever-lish is hard to understand, sometimes I even wonder if they can understand themselves...)
Listen more, Speak more, and Read Out Loud more. It's not something people need to "master" per se, but a tool that one should try to use it as effeciently as possible to communicate with one another. As long it gets the job done, it's all good.