I'm sure we've all thought about this at least once, so lets have some fun with it.

Pretend that we are coming up with a new superhero setting. No DC, no Marvel, etc. A completely fresh start.
Show off that superhero idea that has been kicking around your brain since highschool or whatever. Who are they? What are their powers? What makes them special/fun to read and isn't just another interchangable flying brick with an energy attack? What are their themes that define them? Etc.

We can do villains as well, but villains should never exist in a vacuum, they need to be a foil to a hero to be worth a shit so it makes sense to come up with the heroes first and then find villains that go with them.

Bonus round: are there any 'rules' that we should establish for such a setting that all characters in it are required to follow? Either in an editorial sense (no character lasts more than 20 years, learn to wrap up your character and phase them out to make room for new ones) or a worldbuilding sense (rules for how powers work, etc).