Favorite cheese, favorite color, tv shows, movies, youtube videos, funny experiences you've had, what you did that morning or previously in the day, pets, things that bug you (pet peeves), if you are in school-teachers are a fun one...
Starting a conversation is often easier than it seems. A simple "Hi, how are you doing?" can often launch into an entire conversation, especially if the one being asked has a problem on their mind...
Say "Hello, my name is ___________". Another answer There are many different ways to start a conversation. It also depends on your own gender and on whether you are talking to a lady or a gentleman....
Approach them with a smile and ask them how they are and introduce yourself. If they look at you strange wondering why you are approaching them simply tell them you have seen them around and wanted...