What is the FASTEST method to learn Standard American Accent?

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If you speak a language whose phoneme is not fitting to English such as Chinese, Korean or Japanese, what would you say is the fastest way to learn American accent. I am aware of doing: 1) Listen CAREFULLY. Do not concentrate on the content, but concentrate on speech delivery manner. 2) Bite my teeth when practicing, because Americans move their lips and jaw less than rest of world. Also, Americans speak through the opening between top and lower teeth, and this opening is narrower than when speaking in other accents. 3) Practice all the time. (However, my aim is to get the maximum change in the shortest amount of time possible.) 4) I study with the CD and manual, "American Accent Training." I am beyond the age of 30. Any and all suggestions are welcome.