This is easy! Open the inside bag on your dry cereal ALL the way. This way, you can use a measuring cup to get the right amount of cereal. I found that when I just poured (even into my one cup bowl), it was WAY TOO EASY to get too much. Every 1/4 cup extra adds calories you may not want to eat!
If you are not sure this will help, next time you pour your cereal, measure it AFTER you poured. You might be surprised!