Because the Lemmy community is still pretty small (at least compared to some larger aggregator/forums), it’s hard to know which communities are really active (this goes doubly so when you factor in duplicates across different servers).

I find that browsing /all and sorting by “new” can be a good way to discover the communities Lemmy has to offer (though it requires a decent bit of scrolling to find things you care about).

Hopefully someday, I’ll have found with communities that my subscription page will cover all my interests; but that will definitely take some time.