Rule #1 is Portion Control!
If I were writing a health book (diet book for lack of a better term), this would be the first chapter.
So I have to say that I am currently not following this rule very closely right now, but if you are struggling with your weight or trying to lose those last 5 pounds, this rule is important. Even those that are counting calories, if you are not measuring things out, you are probably under counting your calories. I know it's a pain, but I have to say, I got used to this and don't really think about it much anymore. Once you start measuring everything out, you will then begin to see what a 1/2 cup of rice looks like or 1 cup of cooked pasta and then you might be able to put away the actual measuring cup, but if you see your weight creeping up again, get out the measuring cups again.
Dust off those measuring cups and use salad dishes for dinner plates and you won't even notice the difference except in your waist. :)