How To Speak Like A Native

Indeed, a growing body of evidence points to a “critical period” in childhood for acquiring correctly accented fluency in a given language; even as research on neuroplasticity has pushed the limits of what adults can learn, this boundary has remained stubbornly in place.
http://beaumont.edu.hk/web/eng/program.php?course=174

University of Alberta linguist Tracy Derwing and colleagues divided subjects into three groups: the first received foreign language instruction with no particular focus on pronunciation; the second received instruction with a focus on pronouncing the individual segments of language; and the third received “global” pronunciation instruction on the general way the foreign tongue should sound. After 12 weeks of classes, the students were asked to tell a story in their new language, and their efforts were rated by native-speaking listeners. Only the global group, the listeners reported, showed significant improvement in comprehensibility and fluency.

The intelligibility principle may be behind the acknowledged effectiveness of immersion-learning programs: when we immerse ourselves in a foreign language, particularly as spoken by natives, we’re picking up more than specific vocabulary words: we’re getting the gist of how the language is spoken, and our own attempts reflect this expansive awareness.

Few of us have the time or money to engage in complete immersion, but a good tip is to limit your conversational practice with other native English speakers. The speech of second language learners, research shows, tends to “converge” toward a version of the foreign tongue that is more like the speakers’ native language. Instead, seek out someone who grew up talking the way you want to talk, and practice, practice, practice. You won’t sound perfectly like a native, but the natives will understand you perfectly well.

http://ideas.time.com/2012/04/04/how-to-speak-like-a-native/