A good original species is one that is truly loved by its owner. Cs owners who love and care for their species, expanding them, creating interactive things, doing events, etc., have a better chance of being popular because cs lovers appreciate a well rounded species. ^w^
Even semi-generic species can be popular if the owner is nice, open to talking, and active in their own species. Species with money hungry owners who are never around can be popular for a time but they ALWAYS die out and their cs world grow toxic.
I also think its important to think about what you do. Don't add traits or edit lore to reflect cuteness or popularity if it doesn't fit your species! ^^ And people should not just make a cs out of a cute idea. Maybe do a set of adopts in that style, but like, don't try to make a whole cs out of it if you don't really love it and are inspired.
Ofc, not everything is about popularity. If everything you do for your species involves popularity, then you probably shouldn't run a cs. But those are just my thoughts.