For many recipes to work, you want to stay as close to the listed ingredient measurements as possible. Improperly measuring an ingredient can ruin the recipe, especially in baking when you don't have the opportunity to go back and add more ingredients to cover your mistake or altering ingredients may impact the chemical reaction that occurs during baking.
Tips and Tricks to Measuring
When using dry ingredients like flour, baking power or soda or sugar, it helps to measure them in the appropriate cup (whether it calls for a tablespoon, 1/2 cup, 1 cup, etc.) and then using the straight edge of a knife, to level it off even with the top of the measuring cup. Start off by overfilling the measuring cup and spoon and then level it off. You can do this over a paper plate, which will make it easier to fold and pour the excess dry ingredient back into its container.
When measuring liquids in a liquid measuring cup, it's important to do so at eye-level, so that you get it right on the appropriate measuring line. If you are looking down into the liquid measuring cup, you may misjudge.
If you are using a measuring spoon, it's not a good idea to do it over the bowl you are mixing ingredients in. It's too easy to spill, so measure the ingredient off to the side and then pour into the bowl.