You might start by saying 'Hi.'
Follow that up by asking her a simple question or two, like perhaps her name and where she goes to school. If you already know those, then ask her a question about something you like or think she might be interested in.
"What new movie do you most want to see?" "What did you think of (such and such a show) when (this and that) happened?"
It's not that important what you ask. The most important thing to remember is to ask open-ended questions (those that cannot be answered by a mere 'yes' or 'no') and to take the time to listen to her answers instead of running your own mouth.
Good luck!
