Short answer
Beat the eggs, cook them over low to medium-low heat and fold as curds form. Remove them while they look slightly wetter than the final texture you want.
Heat sets the proteins
As egg proteins unfold and connect, liquid becomes soft curds. High heat makes that network tighten quickly, which can squeeze out moisture and create dry eggs surrounded by liquid. Gentler heat gives more time to stop at the desired stage.
Movement sets the curd size
Continuous stirring produces smaller, creamier curds. Slower sweeping folds produce larger, softer pieces. Both are valid styles. A flexible spatula helps move set egg away from the pan while uncooked egg reaches the heat.
What additions change
Butter or oil changes richness and sticking. Cream, milk and cheese affect moisture, flavour and setting. Watery vegetables should usually be cooked first. Salt is less important than temperature and timing for avoiding rubbery eggs.