Fats prevent whites from foaming properly. This is very important. Make sure all equipment is free of every trace of fat or grease, and that the egg whites have no trace of yolks in them.
Egg whites foam better if they are at room temperature than if they are cold. Remove them from the cooler 1 hour before whipping.
Sugar makes egg white foams more stable. Meringues are thicker and heavier than unsweetened egg white foams, and they are more stable. However, egg whites can hold only a limited amount of sugar without sacrificing volume. For this reason, when making common meringues, many cooks prefer to whip the egg whites with no more than an equal weight of sugar. Additional sugar can be folded in after the meringue is whipped.
Mild acids help foaming. A small amount of cream of tartar or lemon juice is sometimes added to egg whites for whipping in order to give them more volume and stability. This is especially helpful when the whipped whites are folded into other ingredients to provide lightness or leavening, as in the case of angel food cakes. Use about 2 teaspoons cream of tartar per pound of egg whites (15 g/kg).