Aside from what sminkle has said, you may find the following video interesting (if you get offended easily, I wouldn't recommend watching it. The video has some humors that some people might find it offending):
First Step To Getting Rid Of Chinese Accent-Learn Chinese
What I learned from this video is when you are learning a new language, start with a blank mind. Pretend you don't know anything.
I have some books that focus on training American Accent, can't provide any feedback yet since I haven't been working on it. Don't get too stressed even if you can't reach the standard tone :] as long as you can communicate and people can understand without too much trouble, then it is still good you know.