Strive to eat breakfast, pack your lunch, and cook dinner. Avoid buying (unless you already what you are going to get) - It's cheaper and healthier. Look up recipes and make big batches of healthy meals. Divide them into reasonable portions so they are ready for eating throughout the week.
Include lots of whole grains, lean proteins, fruits, veggies, and low fat dairy.
Eat foods that are high volume, low calorie
Don't deny yourself "naughty" foods. Eat a reasonable portion.
Try to find ways to make you favorite foods healthier.