Facebook Etiquette

Living in a small town you tend to run into people. Sometimes these people add you on facebook after never really meeting you. I'm not sure what type of greeting is appropriate, a smile? a hi? a full on "how are you"? Either way I'm not certain, so I just went with a smile and a quick aversion of the eyes. I try not to creep out people and its hard when I semi creep them on the internet, being quiet usually helps me avoid embarrassment though.