To begin with, do not be afraid to ask for help from people that you know. Depending on the scope and magnitude of the event, you will likely not be able to plan it alone. However, select people that you can trust and depend upon. There will likely be a number of things that will have to be managed when deadlines are especially critical. It is at these times when you must have someone that not only understands that the deadline must be met, but someone who has the capacity and dedication to accomplish the task at hand.
Organization is key.
Initially, focus on obtaining the necessary permits if the event is to take place in an area that requires them. Call your city hall or community center and inquire. Tell them the details involved and how many people you are expecting. Be sure to allow plenty of time as the period for issuing a permit may range from a few days to as long as several weeks. Chart out your event on paper.