The first trick is that your egg whites have to be chilled, and the bowl you’ll use to prepare them should be chilled as well.
Add a pinch of salt before you beat them, like this.
Beat them slowly at first, then accelerate gradually.
It's easier with an electric mixer.
If you plan to use the yolks in another recipe, don't forget to store them in the fridge.
Keep beating until it reaches this consistency.
If they're done properly, they won't fall even if you turn your bowl upside down.
If you use an electric mixer, it is much easier.
Move the beaters in circles and turn the bowl as you go.
Be sure to put the beaters and the bowl in the freezer before starting so that they'll be cold, and don't forget the pinch of salt!