How do you make a plain cake fluffier?

To make a plain cake fluffier, ensure you incorporate air into the batter by creaming the butter and sugar together until light and fluffy. Additionally, use room temperature ingredients, as they mix more easily, and consider adding whipped egg whites to the batter for extra lift. Lastly, be careful not to overmix once the dry ingredients are added, as this can develop gluten and lead to a denser cake.