Adding to the niche topic part, and poking @oceanbloom25@lemmy.world to ensure the message is seen, the more one posts to a community, be it yours or others', the higher is the chance of others finding it, though I'd advise against spam and overposting.

If two people from different instances follow a community, the post gets delivered to them in their communities, and that makes the post available to anyone in their specific communities too. If they comment or (microblogging feature) boost, it further spreads, further increasing the chance of more people potentially interested in the topic to join in.

And I suggest no spam or overposting because it becomes annoying fast, making people stay away from the place, and drains your post pool, making for a "drought" of posts which also withers the interest in the topic.