If you really want to speak English with American accent, you have to remember many rules, such as stress, rhythm, vowels, reduced forms, etc. And I think one of the key is linking. When we watch movies, we sometimes couldn't understand what they said. However when we see the English title, we know they didn't say difficult sentence. They don't pronounce each word very clearly. It is hard job to speak English with American accent, but I think it is not impossible. I also need to practice, though.