When initially planning the event, create a big task list with every detail that needs completed for a successful event. Assign the responsibility of the completion of the task to a person/people. Below is an example of a few things that could be on the list:
Right before the event, during set up, have one or two people be in charge. Any person setting up will go directly to them when they need something to do, have questions, or need any help. This point person should be very familiar with the event and be comfortable making decisions regarding how the event needs to be setup.
During the event, it is important to have a detailed schedule for everything going on during the event and behind the scenes (i.e. the schedule has each performance its time listed, but also the time someone has to go to get the food or another activity needs to be set up so it's ready for when it's needed). BuckeyeThon's Dance Marathon Committee creates a schedule in 5 minute intervals of our entire 24 hour dance marathon with every detail in front and behind the scenes. Here's an example itinerary for a Dance Marathon event:
After the event is over, it is important to have a checklist of everything that needs to be done. This could include every room that needs to be cleaned, what needs to be put away, etc. It is a good idea to pre-assign these tasks to certain groups of people, like by committee, so everyone knows what they are doing. Similar to pre-event setup, have a point person be responsible for telling everyone where to go and tear down. This point person can also be the person that approves a task being complete and set a group of students free to go home.