Just start polite and if they seem nice then here's some conversation starters:
-Did you do anything over the weekend?
-What kind of music do you listen to?
-Anything new?
-What classes are you taking? (if you're in school)

If you see someone who's nice then you can start waving to them and your confidence will boost up, don't be afraid to say what's on your mind, no one is going to record it.

If you get nervous from making eye contact, try looking at their nose, they won't know the difference