Community gardening doesn't happen alone; ergo, step one is to find others who share the garden passion. Gauge interest and needs by surveying your target area. Perhaps you canvass the neighborhood and ask your neighbors whether or not they want to join, or you can reach out at your church if you attend somewhere.
Other possibilities include:
Posting flyers on local bulletin boards (like colleges and universities).
Reaching out to your public library.
Even posting online to local message boards and social media groups. You may even find great interest among local civic groups, community organizations, and non-profits.
Your state likely has a master gardener program, and master gardeners share their knowledge and expertise with those who have questions. Find your local master gardener program here:
After garnering sufficient interest, schedule and communicate a day to meet and discuss — whether in person or via teleconferencing software like Skype, Zoom, Facebook, etc. Investigate what skills participants bring to the table, what resources are available amongst the group, and the general wants and needs — whether growing veggies, flowers or both.
Find out who can contribute on regular workdays and coordinate further preparations for the new garden. This moment would also be an ideal time to delegate general responsibilities.
The American Community Gardening Association hosts a central database to find local community gardens or register a new one here: https://www.communitygarden.org/garden