Thank you. Now i know what should i do.

Don't say "Hello."  That is what Chinese people who only know one word say.  It is better to comment about something that is happening around you, even if you only say "Oh, isn't it nice weather we are having today."

Just go ahead and try. I think most of them would be polite enough to talk with you, as long as you are not dressed like a whore :)

你有病吧！最好不要去！全世界都看不起中国人！妈勒批！中国人天生就是贱啊！最好不要打扰人家！

我不太懂你意思。廣州、北京上海都很多外國人，但你隨便找一個外國人去搭訕是有點奇怪。因為你本身是中國人，如果你需要訊息，你更應該找本國人。