When it comes to measuring your ingredients for baking, it's not at all like cooking. Cooking is more of a "little bit here and a little bit there" type of science, where you can add to your personal taste. Sure there are some recipes you might want to chose to keep within a certain guideline, but for the most part, cooking recipes can be played with...
Baking, however, well that's another story. Measuring your ingredients could be the difference between a flat cookie and a fluffy cookie, a dense cake and a light and airy cake, soft & moist muffins or dense and dry muffins...you get the picture.
It is very important to measure correctly to achieve that perfect baked good you are thinking about in your head so when you, or someone you are baking for takes their first bite, they chew with a "Mmmmmm...".
So, here are some tips I've put together about measuring. I think you will find this very helpful.
Measuring dry ingredients such as flours, sugars (with the exception of brown sugars 99% of the time), oatmeal, breadcrumbs and ingredients of that sort, spoon the ingredients lightly into a measuring cup and scrape off the top with the flat edge of a knife, pastry cutter or something like that (I use a pie server. DO NOT shake or tap the ingredients down. That could be the downfall of a moist delicious muffin! Unless it says to "pack" or "firmly pack", this should be your rule of thumb on measuring these types of dry ingredients.
When measuring things such as peanut butter, Shortening (Crisco) or other fats or solids, be sure to spoon the ingredient into a measuring cup and pack it in leveling off the top. These kinds of items are packed as air bubble tend to get trapped within so you wouldn't be getting the correct amount if you just scooped and didn't pack.
When measuring liquids, you should always use a glass measuring cup. Place it on a flat level surface and fill your cup to the appropriate measurement. Make sure to look at your measurement at eye level as looking from above can make it seem like you don't have enough liquid in your measuring cup and you may wind up adding more than what you need.
Here is a little helpful table about other ways you can measure and helpful hints about equivalents.
Well, I hope that helped a little. This can be the difference between the good, the bad and the ugly of baking!