Dry ingredients like flour and sugar are measured in nested measuring cups which come in a set of 4 (1 cup, 1/2 cup, 1/3 cup and 1/4 cup). Sugar and all-purpose flour are measured by dipping the cups into the ingredient until filled then leveling it off with a spatula. For cake flour and confectioners’ sugar, ingredients are spooned onto the cup then leveled off.
Liquid ingredients are poured into spouted glass measuring cups. Placed on a flat surface. Measurement is read at eye level.
Small quantities of dry and liquid ingredients are measured using spoons measuring 1 tablespoon, 1 teaspoon, 1/2 teaspoon or 1/4 teaspoon. Dry ingredients are leveled off with a spatula.
Shortening is measured by pressing down firmly into the measuring cup to make sure there are no air spaces. Brown sugar is also packed firmly to ensure proper measurement. When the cup is inverted the measured sugar should retain the shape of the cup.
Butter need not be measured in cups. One bar of butter is already 1 cup of if you need ½ cup just divide the bar into 2 for 1/3 into 3, and so on.
Source: Complete Guide to Baking