Food Diary - Make a list of reasons why it would be a good idea to write down everything you eat for a week.
I myself have had to keep a food diary on several occasions. Basically in the beginning stages of starting a diet, whether it to be weight loss or weight gain, (I had to gain) a food diary helps you to realize EVERYTHING you put in your mouth. There are many little things we forget that we eat through out the day and this makes us aware of all those we were not counting before. This helps those who don't seem to understand just why they cant loose that last 10 pounds.
Besides creating awareness as to what you consume it also helps you realize any patterns in your daily eating habits, like times of the day you tend to eat or skip meals. This is helpful when meal planning and figuring out how to get the nutrients you need and make it fit in with your busy schedule, since everyone's is different.
Overall I would say it creates an awareness that we probably didn't pay attention to before. I know after I kept one for a couple weeks I was shocked at how much non healthy foods I had consumed when I consider myself to be a health conscious eater and was then able to change that.
Each person is different and this allows you to really understand your eating patterns and weaknesses to ultimately help you reach your goal. Whatever it may be.