Know which foods to avoid and how to activate the metabolism. Having a list of foods isn't enough without explaining what foods aren't on the list but belong there. There literally isn't enough room on a single or even a dozen pages to list all the foods that should be avoided by dieting, but you should generally try to consume smaller portions more frequently throughout the day to keep your metabolism working at all times. Your metabolism is similar to a muscle, in that the more you use it, the stronger it gets.
Cakes and ice cream. While the occasional bite or two of ice cream won't cause you to gain weight, it's the idea that once you start, you can't stop. If you are one of the many who find themselves getting back up to get seconds of cake or ice cream, then you are the ones who need to try eating in moderation. These foods cannot be consumed in large amounts even once per month will put the weight on you after a few years. It's all about having a few spoon fulls in moderation.
Sugar. This is one of the most mis-used and biggest diet busters out there, if you are drinking coffee, chances are you are using way too much sugar. The average american uses more sugar in their coffee then an entire day's recommended consumption, not to mention the junk foods and soft drinks consumed throughout the day. Sugar not only causes higher cholesterol and diabetes, but it also will bust any diet you may be on.
Avoid soda period. Soda falls in the category of addicting and harmful substances in my opinion because of the amount of caffeine that is consumed. People are getting addicted to the caffeine in soda and completely forgetting about the high calories and sugar that is in each can. If the average person drinks 6 Cokes per day with about 150 calories in each, that's about 900 calories just in sodas per day. Not to mention the other foods that are being consumed. Water is a great replacement to soda, you may think you can't switch to water but after you stop drinking sodas and switch to water, you won't even be able to quince your thirst with anything but water or sprite.
Avoid donuts in the morning. Everyone likes the ease of donuts in the morning when they are tired, not to mention the extra pep in their step that the sugar rush will provide but they don't take into consideration that one is never enough. They tend to think that after 5 donuts they have had enough. The problem isn't consumption of these harmful foods but overconsumption. Eating one or two donuts won't hurt you, but If I were on a diet, I would eat bananas or fresh fruit for breakfast instead of donuts which won't provide lasting energy, just a short term sugar rush that will quickly fade and follow with a crash.
Red meats. Many people who are on diets try to eat a lot of white meats because they are high in protein, low in cholesterol and fat. If you are trying to lose weight, you should consume white meats more frequently and red meats way less often but you should still eat red meats in moderation once weekly to ensure you get the proper vitamins that only these meats can provide, but don't eat them more than once weekly in smaller portions.