I spend a lot of time online and I've been in a lot of different spaces over the years — Discord servers, forums, communities of various kinds. The difference between a good one and a bad one is usually pretty clear once you've experienced both, but it's worth naming what those differences actually are.
What makes a space good
Good online spaces have a clear purpose or shared interest that gives people a reason to be there beyond just existing. They have moderation that actually works — not heavy-handed, but present enough that bad behaviour gets addressed rather than becoming the norm. The people in them are genuinely interested in the thing the space is about, rather than just using it as an audience.
The best spaces I've been in feel like the digital equivalent of a room full of people who all care about the same thing. Conversations go deep. People share knowledge generously. When someone asks a question they don't know the answer to, the response is helpful rather than dismissive.
What makes a space bad
Bad spaces usually have a few common features. Drama that recurs and never actually resolves. Cliques that make newer people feel unwelcome. Moderation that's either absent or applied inconsistently. A culture where dunking on people or being the loudest voice matters more than being right or helpful.
Social dynamics that feel more like a school corridor than a place people actually want to be. You know the kind — where status matters more than substance, where certain people can say things others can't, where the point is being seen rather than connecting.
The size thing
Smaller spaces tend to be better. Not always, but usually. A server of 50 people who all know each other is almost always a better experience than a server of 50,000 where nobody does. Scale dilutes quality in online communities the same way it does in most other contexts. The communities I've valued most have been relatively small and relatively focused.
Knowing when to leave
One of the more useful things I've learned is that it's okay to just leave a space that isn't good for you. No explanation needed, no drama about it. Online spaces aren't obligations. If a community makes you feel worse rather than better, or the signal-to-noise ratio has dropped to the point where it's not worth it, leaving is a completely valid response.