Hi 50k,
I see you are concerned with the accent of your English speaking. To tell you the truth, I don't have an American or British accent. My accent is simple and hope local and foreign people can understand me.

So far I have understood that there are a lot of non-native speakers of English outside Cambodia having simple accents, neither American nor British, but they can still make themselves understood.
However, if you are keen to have a particular native accent like an American, Australian or British, it's important to listen carefully and imitate their speaking.

As for me, I try to pronounce words clearly while I'm speaking. And you should try pronouncing each word according to another style you want to adopt. Again, it's not as easy stuff to enrich your accent to be like a native speaker's. You are supposed to go through some years of practice. Listen, listen carefully and you'll catch the points to start on your own.
If you want to listen to American English, go to
www.voaspecialenglish.com. While you are listening it, you can have your own time repeating the words they say.
Just some ideas.
