It really depends on the setting. If you are out at a bar, try commenting on something going on around you like the game on tv or the interesting mixed drink he has. If you are at a party with a group of friends, try talking about how you know the host.
First you must pay some attention to the particular boys you hope to chat with and see what their interests are. It is easiest to begin with things you have in common, such as your school, town, or activities you share in common. Then you can ask about things you have noticed he likes or enjoys.
It depends on what kind of boy he most cases, the sports, political events, cars, wines, favorite books and tasteful food are all good choices.Perhaps the first one is the hottest since most of them are crazy about this.