Here we can discuss anything about this Lemmy instance/server itself.
Our XMPP support chat: Movim or XMPP client.
There is our monthly sticky post that you can comment on with new communities.
Also, since Lemmy-ui recently removed the trending local communities sidebar widget, we are currently thinking about highlighting some communities via the rotating tag lines feature similar to how lemmy.world does it.
Lemmy is by default set to "local", so a lot of users will see posts from a new community, especially if it becomes popular. As for that the key is to simple, short, visual content so basically memes and the like. The other content going well are important news. So if you post those in your community, you might get a lot of interaction. If you want the community to somewhat grow, you probably want to post a lot on it on a regular bases. Then crossposts are important as well. That can bring people to your community.
If you want to promote a community that is on this instance, to other instances, you can post an announcement to !newcommunities@lemmy.world.