The thing that works for me is allowing the pan to heat up quite a bit before pouring the eggs in. I mean, not searing hot, but you want it to make a little "tssssh" noise when you pour in the eggs. Allowing them to sit and cook a little bit before you stir seems to help, too.

That's also why I don't really scramble them very aggressively. The bottom layer needs to sit on the pan and cook, becoming a little solid, before I move them. When I do it that way, they don't stick. It ends up being kind of like an omelette that I frequently ruffled up and then flipped at the end, rather than really scrambled.

TL;DR: A little fat, low to low-medium temp, but don't put the eggs in the pan until it's up to temp, keeping in mind that it'll take longer with the heavy cast iron pan.

When my eggs stick it's virtually always because I was impatient and put them in too soon. If you hear the eggs sizzling from the instant they touched the pan you should be good as long as the heat's not crazy high, but if you dump those eggs in and the pan is quiet than that means it didn't get hot enough in time. It's already too late at that point, they will soak up the fat and stick, but whatever it's not the end of the world. Just wait until it gets hot, throw a few drops of water on there to check if it beeds and floats (good).

What the other commenter said about waiting a moment to start scrambling is good too. I find that if I start stirring while the layer of egg touching the pan is still liquid (which again, can be for awhile if you didn't wait for the pan to get hot), it'll just stir the fat into the eggs instead of around them. So wait just a moment for at least that thin layer contacting the pan to cook before you stir. If your pan is the correct temp it should only take a few seconds, if that.

So yeah, the preheat and the first second or two really make or break scrambled eggs, but past that it's smooth sailing.

I’ve had this problem with scrambled eggs and cast iron. Two things help for me. One is letting the eggs set a bit before I commence scrambling. And the second comes down to choice of spatula. I find that a thin metal “turner” spatula does a much better job at cleanly separating the egg from the pan.

Lower temperatures and more butter/oil or milk help. I have heard keeping the eggs out of the fridge a bit and letting them sit for a bit before disturbing them in the pan also helps but I don’t have time for that and some bits are always going to stick, they just mean you have some nice crispy bits to scrape off and put on top.

You still need grease (butter, oil, or other fat). You may also want to cook it just a tiny bit longer. If they're done, they shouldn't stick.