Mastery means different things to different people depending on their needs. . I am a native speaker of English, but an engineer. I would suspect that only those who study English can ever claim to have mastered it. English has a very rich vocabularly. I use only a small portion of it. There are many words I understand but don't hear from one year to the next. The number I don't know is also large. . I guess the only answer to this is to live it in the way you wish to master it. Reading widely will help with vocabulary. Speaking with others till that becomes natural will aid fluency and pronunciation. . Perhaps the most important ingredient you already have; ambition. . BTW: How can one become a master of the English Language? <-- "the" inserted. English is so obsessed with articles and word-order. one can --> can one for a question the master --> a master, as you will be just one of many, unless, you really mean the greatest master of all, above all others :) English --> the English language, or even the English languages, if you include American :) . Ambition, use it.

The best way: move to an English speaking country. This way you can immerse yourself in the language in your everyday activities. Not everyone can do this, so my second suggestion is to practice it everyday. Speak it, listen to it, and read it. You may not become a "native", but you can become functionally fluent in the language.

I have read on the Internet that 10,000 of hours of practice in any field makes you a master of that thing. Like, 10,000 of violin practice would make one master musician.