Creating Good Communities
Building welcoming spaces is an ongoing processes
On her excellent blog Culture Study, Anne Helen Petersen wrote about the idea of community roadblocks. These are the things preventing us from having active and engaging third places. On her blog Peterson asked
What small or large things make it hard for you to hang out with others in your community - and to just DO THINGS?? Tell us about it.
This is my answer:
I've done a bunch of community organizing for niche/nerdy hobbies. The biggest roadblock I've found is finding safe like-minded people to spend time with. A lot of people (aka a lot of men) are harmful to the communities they're in. This can be actively harmful (predatory or bigoted behavior) or more subtly harmful (dominating conversations, microaggressions). So the difficulty is find people who share your interests AND share your values.
My solutions this are signaling and moderation. Signaling means branding your community in such a way to attract the people you want to hang out with. In my case, it means putting a rainbow flag in the logo. Or intentionally calling the event an "inclusive space". Subtly and not-so-subtly signal who the event is for and who it is NOT for. This sets expectations for the community.
Moderation is the other side of the coin. Once you've started the community you need to guide it in the right direction. Model the behavior you want to see in the community. Maybe this means putting pronouns in your user name. Or using inclusive language when speaking to the community. But it's also going to mean stepping up when someone is causing problems, intentionally or otherwise. It helps to have a written code of conduct, so you can point to that and say "We don't do that here."
This is always going to be an active process. People naturally drift away from communities over time. This means you'll always need to be doing some level of outreach to keep the community stable. (This doesn't mean advertising, it could be as simple as inviting a new friend to the group.) But this means the signaling and moderation is a continuous process.

