If you do happen to get some egg yolk in with the white, remove the unwanted yolk by using an empty eggshell. Egg yolks will immediately start to form a skin after being separated. Cover the yolks with plastic wrap, if you need to bring them to room temperature before using. Always use the size egg that is called for in the recipe. If the size is not given, assume it is large.
Most eggs used in baking are at room temperature.
A quick way to warm eggs to room temperature is to place them in warm water for 10 - 15 minutes, or else leave them out for an hour.