Cold eggs are easier to divide
A chilled yolk is firmer and its membrane is less likely to break. Separate eggs while cold, then allow the portions to warm only if the recipe benefits from it. Set out three bowls: working white, yolks and completed whites.
Choose a method to suit the job
Passing the yolk between shell halves is quick, while clean fingers give good control and reduce the chance of a sharp shell cutting the yolk. A separator is useful for volume. Work over the small bowl so one broken yolk does not spoil all the whites.
Know how clean is clean enough
A trace of white in a yolk rarely matters. For meringue, however, even a little yolk fat can reduce foam volume. Transfer each clean white to the main bowl before starting the next egg.