- Rachel's English, both the [Youtube video](https://www.youtube.com/user/rachelsenglish/videos) as well as her [online course](https://rachelsenglish.com) - ELSA Speak, an iOS app that is great and whose pronunciation detection algorithm is uncannily good. The app design could be better, but it gets the job done and it makes me practice and learn what I'm doing wrong. However, I struggle to use it every day.
I'm open to finding new methods, but I generally find the available ones either too naive or too time consuming.
Think of a Japanese native speaker listening to English. The L/R sounds don't really exist in Japanese, so they sound the same. You can say "copy this sound" as much as you like, but if someone can't discriminate between the sounds in the first place then it's very difficult to copy. Practicing with minimal pairs (words that differ by only a single sound) can help build the ability to hear the difference between the sounds. Fortunately, this is not such a big issue for learning accents in your native language: If you can hear the accent you can hear the sounds.
Reproducing the sounds comes next. Learn about vowel placement. Learn IPA. Listen to snippets of the target accent and try to pinpoint what particular sounds make that accent that accent. Practice producing those sounds, recording yourself and using those hearing skills to notice if you are creating the right sounds.
Finally, you've got to put them all together into an integrated performance that becomes an accident. People doing "bad accents" are usually doing one or two key words and then slipping back into something much closer to their regular accent.