Try to speak to native speakers on skype or somewhere else where you can use a microphone. Or watch a lot of English language TV and movies and try to repeat what you hear until it sounds the same. You might also want to try recording yourself and playing it back to see which sounds you are pronouncing incorrectly. Mostly you just have to make sure you know what the correct pronunciation is and then practice it a lot! :)

see my notebook entries on my NLLS

I think accent is so hard to change.