Before

Pick the date and commit to it publicly, three to four weeks out. Late spring evenings work best in most climates. If your country already observes a Neighbors' Day, use that date. In the US, you can use National Good Neighbor Day which happens September 28.

If you are doing it in a building, claim a semi-public spot nobody owns: the lobby, the courtyard, the stairwell landing, the parking area, or the wide part of the sidewalk. Ask the building manager or landlord, who will usually agree because it costs them nothing and makes tenants happy.

Create an event in Plurality and print your flyer. Put it on every door and in public spaces. Say bring a dish or something to drink, nothing more.

During

Keep it potluck and keep it cheap, so nobody is a host and nobody is a guest. Let it run long and let kids run around. And give the folks who only stayed fifteen minutes full credit; they came, and next year they'll stay for an hour.

After

Take a photo of the party and invite folks to record any other Moments.

Then convert one evening into a habit: propose something small and monthly before people disperse, a coffee in the lobby or a walk. And tell the building next door how easy it was. Périfan's version scaled because one courtyard's party is visible from the next courtyard.