What are the dos and don'ts of flirting with strangers in public?

I’m not talking about bars or clubs. I mean places like bookstores, cafes, grocery stores, or laundromats.

My question is for both the “hunters” and the “hunted”, so to speak. If you’ve successfully approached an attractive stranger in a situation like this, how did you do it? If you’ve been the recipient of overtures from a stranger, how did you respond and why?

If you are unattached but would still prefer not to be approached at all in places like these, your view would interest me too.