cereal
Usually i greet them and have a little small talk like "how are you?" or "how's life?" and things similar like that, just ask what you want to ask, go elaborate. if you know what their hobby is then you could start by asking things about, let's say, "why do you like to (their hobby)?" or "who's your favorite singer?" and lots of things. one thing for you to must do is to not make it look forced or else it would be awkward.