What does it mean to be a good citizen on the Internet?

Hmmm good question...
Honestly I think it’s up to your etiquette, morals, and ethics. There’s no absolute correct way to be a “good citizen” on the internet in these modern times. Just gotta be cautious because there are people out there to get you, your belongings, or even your identity.
Others may perceive one person as good, but another person may perceive that same person as bad.
It’s all up to you. It’s on your perspective. Perception is reality after all.