The fastest way is hiring a teacher or a tutor, of course. But also you could use some audio courses. For example, Pimsleur's or Hoge's versions are very good. Doing them carefully you even could have a clear pronunciation.
Simple: Find a native English speaker from New York City or Chicago. I happen to be both: (1) born in one (NYC) where grandparent lived and so visited annually over many years; (2) raised, from age of 2 years to around 17 years, in Chicago -- IN the city, not its suburbs.
I can speak English VERY quickly... hell, it's @ times difficult for me to remember to slow down when conversing withe my Russian, Ukrainian, and French friends w/ whom I am having English conversations for their English conversation "practice".