Tones
Everybody knows there are tones in Chinese. Every time when I taught Chinese to foreign students, they would say it was difficult to tell all the tones.
Tones (From Pinyin wikipedia)
Even though I taught Chinese, I still did not figure out how to explain the difference among them using worlds. Every time I just try to demonstrate the difference in front of everybody.
Maybe that is way to learn that. First you listen to the right one, and then remember that and then practise.