1. Get the leadership of your congregation on board. Ask them to manage the communication to church members and to assist with hosting (ushers, greeters, refreshments if provided, etc).
2. As you do this, share whom you are planning to invite, and ask them to identify whom you may be leaving out and for any other contacts with other community leaders they may have. Decide together who will commit to contact these persons.
3. Create a diverse core team of community leaders (probably pastors, rabbis, imams, mayor's office reps etc) to determine time and place for the event and to help get their wider constituencies on board. This team needs to choose a point person who will coordinate the other teams and make final decisions.
4. The point person names and publicizes a single point of contact (one person) to manage all communications with the wider community about the event. Provide at least three ways (phone, email, social media location) to contact the contact person.
The point person generally should not be the contact person.
The role of the contact person is not communications/marketing but rather gathering names of attendees and leaders confirmed and giving reliable information about the event to the wider public.
5. Point person keeps asking "who is not here" and finding contacts to invite them and as appropriate include them in the program.
6. Point person forms a steering committee (SC, 3 max) to do the core groundwork of designing the event itself (what happens in what order and by whom). The SC should produce a complete tech script with every cue for every stage action and the technology actions needed (which mics, what sound levels, which lights, what slide, what camera and camera angle) for the entire service. Tech crew need this info ASAP. At least 24 hours in advance is good.
7. Point person forms a small marketing committee to run invitation/marketing of the event to the wider community through multiple means (phone, email, social media, radio, TV and newspapers as available).
8. Point person gathers all leaders for the event (any who will be on stage, including music groups, sound, lighting, graphics and video crew, as applicable) at least 1 hour before the doors open for a cue to cue rehearsal. This is not a complete run-through, but a rehearsal of key transitions so all know where and how to move and tech folks know what to expect and how to adjust/position sound/lighting/cameras when the service actually happens.
9. Run the event.
10. 15 minutes after the event, point person gathers key leaders (tech, major speakers/performers, marketing and communications reps, congregational leaders) for a debrief of where they saw God at work first of all (HT Barbara Day Miller), then after ample time for testimony, a breakdown of what went well, what you learned by doing this, what you can do better next time and how.
Feel free to add to this list from your experience in the comments below.