Didn't your parents teach you not to talk to strangers? Lol
Seriously, though. It would be good to start off by introducing yourself, and asking their name.
How do you talk to a stranger? (in school)
If your chatting student is stranger one,first you should start your talk with statement "Excuse me " .Then introduce yourself and then ask their name. Collect all the information about that student.And then ask help for your needs if you have.After get it ,say "thank you and see you again".You should behave politely to other person, even if that person is student.
