Muscularity, tonality, point of resonance, articulatory settings: American Accent

I remember seeing a story of someone who wanted to be an actor in the US, but had a think Eastern European accent. He hired a vocal coach to teach him... the coach suggested putting a small piece of cork between your molars in the back of your mouth. He said this greatly helped his accent. Apparently it has a lot to do with the placement of your teeth, tongue and jaw. tl;dr Put cork in between your molars, bite down, sound american. Profit?

 I'm American, and actually, I kinda understand what you're talking about. After having myself and co-workers try talking with a pen in their mouths, they sound...like, ultra-American somehow. I don't really know how to describe it other than that.

American here, when I studied abroad in France my host mother told me that, "The English always take great care to pronounce every letter. Americans always sound as though their mouths are full of potatoes." 

Another tip, from a linguistics student:
A lot of your consonants are probably retroflex, which means that your tongue is curled back when you say them (for example, the English [l] and [r] are retroflex, but no other consonants are). Try saying your consonants the way you normally would in your accent, and then try it again but this time straighten out your tongue (so instead of the underside curling over and touching whatever the part of your palate it is, the top side is touching it). 

I went to see a Sam Shepard (American Playwright) play in England a few years back. After the play there was a Q+A with the actors. During the play I could have sworn they were all American, but afterwards they all had cockney accents. One person asked how they did American accents so well. The trick, apparently, was to stick a piece of gum in your mouth, take a couple of chews with your mouth open, and then start talking. Similar concept I am sure.

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• It is not so much about retroflexed consonants that many Indians use (like t and d). The pen/cork trick is to the bring the 'tone' of American accent: esp, to elongate and compress vowels on demand.
• Whispy and bone prop: Check here