How to ensure a successfully run event? The answer is simple, beforehand communication from the event organizer with every helper of the event, in a thorough, clear, and concise manner, is the key.
If the event has a host, both of the event organizer and the host should be fully clear on the entire run through of every aspect of the event.
Contingency plans should be in place to deal with the occurrence of the unexpected circumstances. Aside from making sure that all helpers of the event understand their duties and what is expected of them, the event organizer and the host should come up with a strategy, in terms of how to deploy contingency plans in a subtle, yet efficient manner without notice of the event attendees.