Tip is to feature it on the [email protected] community, crosspost the first few posts from there to more popular communities, and be sure to link various discussion threads from that community in other communities. Get people interested enough to Subscribe then posts will spread to that instance.
This inconvenience is partly by design in Lemmy. People that start up a new server don't want to have ALL the content across the Fediverse rush through and explode their PC or hosted VM. Or a troll that makes a new community, spams a bunch of posts or puts up illegal material in a new community can easily be caught in the home instance before it spreads to others.