When using dry measuring cups, it's important to select the size cup (or in the case of 2/3 cup or 3/4 cup, two cups must often be used) with the exact capacity called for in the recipe. Then fill the cup even with the top rim.
Dry ingredients such as flour, grains, crumbs and granulated sugar should be stirred before measuring, then lightly spooned into the cup until it overflows. Do not tap the cup and pack the ingredient down. Level the ingredient with the rim using a metal spatula or straight-sided knife.
It was necessary in the past to sift flour to remove lumps, but today, unless the recipe directs, flour no longer needs to be sifted before measuring. Most sources, however, recommend sifting powdered sugar to achieve the most accurate measure.
When it comes to brown sugar, it should be packed firmly into the cup with a spoon so lumps are crushed and it retains the shape of the cup when removed. Shortening, butter and other dense ingredients also need to be packed into the cup to remove any air space. Use a rubber spatula to pack and level off these ingredients.