Choose Nutrient-Dense, Low-Calorie Foods
You can cut calories by either eating smaller amounts of calorie-dense foods (the ones that got you fat) or by choosing foods that are low in calories, but rich in nutrients and fiber, like fruits and vegetables. When you eat nutrient-dense foods, you can eat a large volume of food, so you don't feel deprived. Maybe today the idea of eating an apple rather than a donut as a mid-morning snack doesn't sound appealing, but you'll get used to it.
I replaced the greasy, sugary foods I liked as a young adult with fresh fruits, vegetables and nuts, and I cut back on fried foods and processed meats. It wasn't easy at first, I missed the junk food for a while, but today I'll take a crisp, sweet Gala apple over a greasy, icky donut any day.