Honestly at this point there’s a fairly large number of instances so yours would need a selling point to even begin. And that’s before taking things like owner behaviour and strictness into consideration because the instance theme and tools will always be the first impression.
“Generic catch all instances” are common. You can only build up a user base if existing people are willing to ditch their own. What are yours doing that the current ones do not?
Do you have a focus on a particular topic? I would consider posting a beautiful photo that I took on an instance dedicated to photography rather than the catch all one.
Is your UI unique/pretty? Which leads me to the next point…
Do you offer certain tools available/unique to your instance? 1) If yes, why can’t they be integrated with base lemmy? It’s open source after all. 2) If no for whatever reason (Lemmy devs slow to respond, low on their priority, will not accept, I don’t agree with their behaviour etc) is there a reason it cannot be included on other existing instances? Why is it exclusive to yours?
And then I would start looking at the details like what would uptime be, how much are you yourself making an effort to contribute and expand, etc