Learn how to measure correctly. Have the right tools for the right job.

All measuring cups are not the same. Use different ones for dry and wet ingredients.
Dry measuring cups: use to measure flour, sugar, and all dry ingredients. Use the size cup needed for measurement, 1 cup, 1/2 cup, 1/3 cup or 1/4 cup; spoon into cup and level off at the top.

 

Measuring liquids: Use a clear measuring cup with a pour spout. Pour liquid in and get at eye level to make sure measurement is accurate.

 
Using measuring spoons: Have a set or two of measuring spoons handy. Measurements are always level; level off with a flat edge if the can does not have a self-leveling edge on it. If you are measuring wet ingredients, and dry ingredients with the same set of spoons, make sure the spoons are clean and dry before measuring the dry ingredients. Be especially careful when measuring baking powder because a wet spoon inserted into the can will start a leavening action; the baking powder may not work well the next time you want to bake.