I had this same question several months ago. Here's what I've found:
1) Even with the "non-stick" qualities that build up, I still use a (usually very) small amount of fat every time. I'm partial to bacon grease or butter. If I'm frying an egg, I'll use maybe 1/8 teaspoon, and most of that stays in the pan--when the egg goes in, the grease gets pushed outwards, with a tiny layer under the egg.
2) once you put the egg(s) in the pan, DON'T TOUCH THEM until you flip them. I often cook a mix of hash browns, crumbled sausage, and eggs in our cast iron. A bit of oil/butter/grease for the hash browns at the beginning, then add the sausage and brown that, and then I pour the eggs on top and
leave them alone. When the eggs are solid enough I flip or fold them. In short, don't stir your eggs or poke at them while they're cooking, and use a bit of fat at the beginning, and it'll be fine.
I thought the point of cast iron over, say stainless, was that once it's well seasoned it's not necessary to continue using a lot of oil while you cook?
I had better results frying an egg yesterday with letting the pan get hotter before adding the egg and using a different spatula. As for grease, I used a very little bit of tallow I rendered from a beef heart. I've been ignoring the spatula, but the one I usually use is too big to easily fit in the little egg skillet. Will continue experimenting.
You certainly still need to use a
little oil, but it's definitely not much. This is doubly true if you properly clean it and give it a very thin coat of oil after each use.