Benny has an excellent, brief answer.

Here is some additional information.

-1- Generic English. American English and British English vary slightly. There are small differences in grammar and vocabulary for the standard (mass media) dialects of American English and British English. English Grammar in Use has a two-page appendix for the differences.

-2- American accent. There are regional accents such as the New York accent, but the standard accent, General American, is characterized by a pronounced R /r/ in all positions and an unrounded back vowel "ah" /ɑ/.

Here is link to an accent coach giving a very brief demo of how a British actor can sound "American" on stage.

<a href="https://www.youtube.com/watch?v=p5T3ubSdhSM" rel="noopener noreferrer" target="_blank">https://www.youtube.com/watch?v=p5T3ubSdhSM</a>;

-3- Reducing first language interference. All language learners bring their first language grammar and pronunciation patterns to their second language. With time and effort, the language learners achieve a good approximation of the second language. The goal is to be understood. Sounding like a native speaker is nearly impossible for an adult.

For American English pronunciation, Russian and Ukrainian speakers usually need to work on intonation, on W /w/ and V /v/, and on the vowels in the following words: beet /i/, bit /ɪ/, bait /eɪ/, bet /ɛ/, bat /æ/, boot /u/, book /ʊ/, boat /oʊ/, but /ʌ/, bot /ɑ/, bite /aɪ/, bird /ər/, bored /ɔr/, boy /ɔɪ/, bout /aʊ/, and "uh" /ə/.

Working on TH /ð/ and /θ/ is relatively unimportant. Most non-native speakers substitute a similar sound and everybody understands.

-4- Pronunciation lessons. The "repeat-after-me" method is traditional but ineffective. Pronunciation specialists (certain English teachers with a linguistics background, linguists, and speech therapists) have a detailed knowledge of articulatory phonetics. They can help students put the tongue and lips in the correct position to produce a desired sound.

My professional experience is that ten hours of pronunciation training make a dramatic difference.

First, let's define the "accent." For me,

Then, let's define "American Accent." Most (American) dictionaries, pronunciation/accent reduction courses are modeled after "General American" accent. It's the accent of people in the midwestern United States.

In order to improve your pronunciation, you need a couple of pronunciation books + a qualified teacher and about 1-1.5 years to double-check words you already know with dictionary.

The complete elimination of foreign accent probably takes ages to learn, it's almost impossible for non-native speakers.

Having an accent isn't bad. It depends on how strong your accent is. If it is so strong that it makes your words unclear then that's when it becomes a problem. That's when American English speakers may have difficulty understanding you. But a mild accent isn't a bad thing at all.

   Thank you all for the answers, very informative.

I was born in Chicago and when I moved to a Southern state I just listened very intently to people here. To their accent. I just picked up the accent without doing anything more than that. My niece who was 8 when she moved picked it up much more than me since she was in school here and heard it constantly. People I think will find you more interesting if you keep your accent