There is Liquid and Dry measurements, be sure you use the right tools for the job. If a cup of flour in a dry measuring cup, and one cup of flour measured in a liquid measuring cup were weighed, the weigh would be different. It is very important to read the recipe and follow the directions, if it calls for 1/2 cup packed brown sugar, you must be sure to pack the brown sugar, for the right measurement.
Always use proper measuring spoons. Baking is science and each ingredient and measurement will affect the out come.