I learned by watching my favorite shows. I would just rewind and say the words back, until they sounded right to me. I never studied the American accent, in terms of getting a teacher or taking phonetics classes. I've always been a good mimic. It really wasn't that hard for me.
I'm aware now over the last 5 or 10 years that when you do an accent, you really have to kind of get down to the nitty gritty and go into the phonetics of it, if necessary. Find out not just the sounds but the rhythms and the music - or lack thereof - in a particular accent.
Acoustic phonetics, which is developing and increasing in richness very rapidly, already enables us to solve many of the mysteries of sound, mysteries which motor phonetics could not even begin to solve.
In college, I went to school for acting; we had to learn phonetics just to be able to do dialects and all that stuff. I'm somebody who does better just hearing it. I'll just imitate it, and I get it better that way. When I know too much information, I'm not great.
The best scheme of Phonetics is a stiff uncertain thing.
Semantics, or the study of meaning, remained undeveloped, while phonetics made rapid progress and even came to occupy the central place in the scientific study of language.