Before the start of each event, find the time to connect with your volunteers. Getting to know them and their skills can allow you to better discern their roles and also build stronger rapport for teamwork, thus ensuring that the event is smooth and enjoyable for all. 

Alternatively, you can also place volunteers in their designation and groups and get them to intermingle, play games, or get acquainted with one another before the event commences.

Such sessions need not be long, and can take 15-30 minutes prior to the event. You can also consider having senior volunteers lead such sessions to allow them an opportunity to enhance their leadership skills.