Eric Holscher:

…most events develop an “insiders” group who’s been going for a long time. These groups tend to feel like exclusionary cliques for first-time attendees, and actively hurt the community’s goal of inclusion. I’d like to propose a simple rule that we have at the events I run, which I think makes inclusion easier for everyone.

The rule is: For every year you have attended the event, you should try to meet that many new people each day.
An example makes it clear: If you have attended this event for three years, you should try to meet three new people each day.

Event organizers should be reading and promoting this article to EVERYONE involved in their events. The outcome of implementing this concept speaks for itself.

New people only have to meet one new person each day, a useful and attainable goal
People coming back for the second or third year feel a bit more responsibility to be stewards for the community, a valuable role for them to play
The organizers and long-time attendees need to meet the most people, and they are the most valuable in spreading the culture of the event – they are also the most exciting for new people to meet!