Two key principles for successful events are organization and scheduling. This is doubtless no revelation. However, all too often these principles are ignored by beginning, and sometimes even experienced, activists, and events are rushed and pulled off half baked. While this is not always disaster, and often is the only way it could be done, one should always attempt to allow for as much time as possible for thoroughly planning of major events. Form committees for different parts of the list.
Delegation is critical, as is sufficient supervision.
Set your goals sufficiently in advance to allow for Murphy and his minions. An effective activist works with as many existing resources as possible. Get to know your local green and health activists. Coordinate event calendars to avoid conflicts and consider sharing resources such as media and activist faxlists. Even more important is outreach to the local community outside the activist fold.