The equation for weight loss is rather simple - calories burned needs to be higher than calories consumed, so you are in a calories deficit. So when cutting back on the calories you want to find foods that are filling and that are not loaded with calories. Basically you want to look for foods with high water and high fiber content, since they add bulk to your meals and fill you up without adding a lot of calories.
Adding more low-calorie, high-volume foods is considered the "volumetric" theory of eating, which has been studied extensively at Pennsylvania State University. The basic recommendation is to begin a meal with the classic starters of soup or salad, aka liquid and bulk. Just make sure the soup is broth base and loaded with veggies and always go easy on the dressing. Salad dressings can be loaded with fat and hidden calories.