Chatting up strangers?

Some of you mentioned that they sometimes approach "Chinese-looking" people on the street/in restaurants etc.. I'm determined to give this method a try. Is it likely that they will actually react positively? I'm probably not the most outgoing of persons so I'm interested in suggestions for good conversation starters that won't offend my prospective interlocutors. (And what to do if they're Korean/Vietnamese or only speak Cantonese?)