"Hey, I noticed you standing/walking/emulsifying/spontaneously combusting and I thought you were cute so I had to come say Hi. I'm Richard."
"Hey, I'm a little lost right now. My map says there should be a coffee shop around here but I can't find it - any idea where Cafe de Lucca is?" to get the ball rolling.
You can tie it in to the context of the situation or you can go direct (going direct is my style but it's a bit higher risk at the benefit of being a little more flexible and widely applicable). In any case, you have to start the conversation and the easiest way to do that is with a "Hi" or some derivative of
-Richard