1. Don't skip meals. If your body thinks you aren't feeding it it will learn to hang on to every calorie that you do eat, and will have trouble burning off calories. Make healthy muffins or something that will last a while if you know you skip breakfast frequently or some other strategic way to make sure you aren't skipping meals.
2. Drink water! Keeping the body hydrated is important!
3. Don't eat only diet foods. They can mess with how your body processes calories.
4. Make sure you get enough iron. When your iron is low you can become tired. This will make you less motivated to exercise!