A lot of people want to learn a native American or English accent.

It's not really necessary to do that, but it's kind of a fun goal. To be honest, with the
right techniques it is possible to get pretty close.

There are really 2 things you need to do. Listen to native speakers and record your own voice.

Listening to Native Speakers
If you want to sing your favorite song you would listen to it often and try to copy it. You wouldn't just read the words to the song. You would listen and copy, listen and copy. Even if your song isn't exactly like the professional, it will get better and better. It's obvious that this is what to do when singing. For some reason, this is not how people study English. If you want to sound like a native speaker, just listen to them a lot. This is exactly how they learn. British people have a perfect British accent. They have no choice. Americans have a perfect American accent. They never learned it. They just listened and copied. It's as simple as that.

Record your voice and listen to it.
Sometimes how you think you sound and how you actually sound are quite different. It's a weird feeling to record your own voice and listen to it, but the weird feeling goes away quite quickly. You need to hear yourself so you can correct your own mistakes. Alternate between listening to native speakers and yourself. Compare and practice saying the words and sentences that give you trouble. You'll notice that some words are better than others. Work on your weaknesses.
Most people don't study this way and as a result have a poor accent. Follow these two steps and you'll improve a lot in a short time.