The main favourable qualities to select a head boy are: 
1) Good communication skills-  But also listening is a big part of communication and you need to identify when someone needs to be listened to and you need to be able to do that.
Confidence- you should be able to talk to all with confidence.Example- teachers,pupils......
Problem solving ability- you should be able to think and figure out solutions for any problems faced,moreover, the solutions should be more effective.
4) Responsibility- As a head boy, you will be in charge of a lot of things as a very responsible person.
5) Leadership qualities- you first need to be an adaptable leader.You should have the courage to lead your team.........

These are the qualities which i used to elect a new head boy.