There are five basic methods for cooking eggs.
The basic principle of egg cooking is to use a medium to low temperature and time carefully. When eggs are cooked at too high a temperature or for too long at a low temperature, whites shrink and become tough and rubbery; yolks become tough and their surface may turn gray-green.
Eggs, other than hard-cooked, should be cooked until the whites are completely coagulated and the yolks begin to thicken.