This tip goes hand in hand with the previous one, Think About the Food You Eat. I think we all tend to lie to ourselves a bit about the things we eat in a day. We also may not realize how many calories are in a particular food, or just how many (or few!) calories we should be eating in a day. A food journal is a great way to hold yourself accountable. I use MyFitnessPal, both the website and the iPhone app, to keep my food journal. There are many other food journal apps and websites, and of course you could just use a pen and paper.
You can just keep a journal for a short time until you figure out where your problem points are, and to get a better understanding of the calories in different kinds of food. Or you could log consistently over a long period if you need it to keep yourself on track. Do whatever works best for you, and that may change over time.
I have been keeping a food journal on and off for over a year. I stopped logging for a few months in March when I felt like I had a really good grasp of how to continue losing without it, then started logging again after a busy May when I hadn’t lost any weight and only had a few pounds left to reach 100 pounds lost. I managed to drop the last few pounds pretty quickly once I started logging again. Now that I am considering going into maintenance, I am taking a break from logging again. If I find the weight is going back on at any point, I know I can start logging again to figure out what I am doing wrong. Instead of seeming like a burden to me, I find keeping a food journal (even if it is only occasionally now) gives me confidence in my continued success.