If it's a short conversation. Where are from, what do you (for work or hobbies), what brought you here and who are you here with. If you both answer the questions this is about a 5 minute conversation that will help you feel comfortable with the person and ask more questions based on how they answered.
If they are friendly, then continue asking questions. Otherwise, say goodbye and have a nice day. Also note, this should be a natural conversation, not a rapid fire interrogation :)
Good Luck.