I cheated the system and just politely usurped an existing comm with a few hundred subscribers thanks to prior Reddit fame! 😇
On a more serious note, I was telling someone today that I mainly try to give them content they won't be able to get anywhere else, including on r/superbowl. I filter through the hell of Facebook to pick out things they don't want to sort through, or I do summaries of research papers they don't have time to read. I search for sources of content with small audiences.
I also try to engage with everyone that replies to me. I value all my commenters, and them chiming in grows the group as much as me posting, so I want them to feel like kings and queens for participating so they come back. They can go anywhere for content, but they gave me a chance, so I want them to come back to me first next time.
Owl of the Year was also a big 2 or 3 week event that really picked up steam quickly, and will hopefully draw people back again this year. Not sure how replicable that is for most of you, but I'm glad I tried it.