Egg whites can be whisked to as much as eight times their volume. It helps considerably if they are at room temperature and only a few days old. Stale whites will never whisk properly. Egg whites should always be whisked just before you want to use them otherwise they will begin to collapse and weep very quickly. Adding a pinch of salt or cream of tartar at the start of whisking will help to make the whisked whites stiff.
A balloon whisk and a copper bowl will produce the stiffest egg whites. The copper appears to have an effect on the egg whites, making the beaten foam more stable.
If you do not have a copper bowl, use stainless steel, glass or china and an electric mixer. Whatever utensil you use to whisk the egg white, it must be free from grease and traces of egg yolk.