If you bake a cake from scratch, which is much better than from a box, you often follow these steps:

• Cream butter with sugar
• Add some fluid [such as milk] with dry ingredients [flour] in alternating steps

Why do you have to alternate? And why do you begin with the dry and end with the dry?

It’s all about the butter. That whipped butter and sugar mixture cannot absorb much liquid. If you began with liquid, or worse added all the liquid, the butter will become saturated, the batter will separate, and the liquid will stay on top. At that point, adding dry ingredients will absorb  that liquid but the resulting batter will be wrong and the cake will be heavy. You’ll have tasty concrete, not subtle cake.

So, follow those instructions and begin with the dry, alternate with the liquid, and carefully craft your batter. After each addition of the dry ingredients, mix only until most of it is incorporated. Some streaks of dry are fine. If you try to get every round of dry ingredients totally incorporated, you’ll begin activation of the gluten in the flour. Your cake will be tough, not light.

Information Source: Perfect Cakes by Nick Malgieri