[jliechti1]

Here's how I did it:

Listen a lot, as often as possible. Watch TV and movies - there are many on Youtube and Youku. I like to convert interviews from Youtube into mp3s and listen to them during the day during down time. Pick a character in these shows and try to imitate their accent (stick to someone your own gender). Try not to read the subtitles (even the Chinese subtitles).

If you want to go further, strip out voice clips from these TV and movies and put them into an SRS system (Anki, Mnemosyne, etc...).