Totally agree, besides

Ann Cook's comment below can serve as a genral guidance for American English pronunciation.
One of the main differences between the way an American talks and the way the rest of the world talks is that Americans don't really move their lips. Americans create most of their sounds in the throat, using our tongue very actively. If you hold your fingers over your lips or clench your jaws when you practice speaking American English, you will find yourself much closer to native-sounding speech than if you try to pronounce every ... single ... sound ... very ... carefully.