I was working a dance event, technically a rental, and had the chance to see a dance event by youth for youth that was successful. Here's what I learned:
Nothing like the presence of peers. The group had a youth staff of about 20 that organized the event, and was running the event on-site. There were two advisors of the groups, plus about 4 parent chaperons, and two off-duty officers, but the event logistics were handed by these teenagers. The effect it had was amazing. The youth attendees, knowing they were being watched by their own peers, and that any trouble they got into would be causing trouble for their own peers, was a powerful force in keeping the peace. The youth staff was not shy about asserting their presence, which is an important way of establishing themselves as a source of reputable authority which their peers could understand and respect. They wore event staff shirts, black with bright neon print, and were constantly around and visible event if there were not currently staffing a position (they worked on a rotation shift schedule).
First response, and clarity of roles.These youth staff members were also able to recognize trouble in its early stages and get them out of the crowd, and to somebody better able to handle it. One girl attended reeked a alcohol, and the youth staff member immediately pulled her aside and passed her off to the off-duty officers, advisors, and myself. This youth staff member understood that their role was to keep at her postilion doing coat check, and to serve as a filter. By understanding what was in and what was out of scope for her position, this youth staff member was able to contact the appropriate staff to handle it. Secondly, by getting the girl off to the side and removed from the crowd at large, it isolates it problem so that others are less likely to get involved and blow up the situation. This is crucial to preventing the problem from getting out of hand.
Support, but empower. The event went so smoothly not because there weren't problems, but because it was handled quickly and cleanly by everybody that was present. By empowering the 20-some youth staff members to plan and execute an event that meant a lot to them, it made them vested into the outcome of such an event. The advisors only advised them in plan the event logistics and chaperons were only present to support the youth staff and stayed upstairs (the event is confined within the downstairs space). Giving the responsiblity of running the event and keeping everybody safe to these young stakeholders, while making sure to support them as they learn how to, is what made the actual event itself so successful (from the security point of view, and they also made a profit to be donated to charity!)