The average woman needs approximately 2000 calories per day and the average man around 2500 calories per day. When you are excercising, you will have to make sure you keep your intake below this average. Eat less, but also healthier to make sure you do get the right nutrients. When you are very active, you will burn more calories and you will see results quicker. In both situations, it's all about CONSUMING LESS calories and BURNING MORE calories.
Think before you do
According to calculations from Harvard Medical School, a person who weighs 83 kilogram would burn around 200 calories when they are walking at a 6kph pace. It's easy to undo this workout by eating just four chocolate cookies, one and a half scoops of ice cream, or two glasses of wine. Even the effort of an intense bike ride, where you might burn up to 700 calories, can be neutralized by eating a piece of pie or drinking a beer. It's actually quite unfair how much time you need to burn the calories to allow such small amounts of delicious treats. Of course not all calories are the same, but for the sake of simplicity, let's say 3500kcal equal around half a kg of fat. This means, in order to lose half a kilogram per week, you must cut 500kcal of your daily food intake. When you drink soft drinks, this is the easiest thing to cut back on. It's a cliché, but true at the same time, losing weight gradually (half a kg to 1kg per week) is the most successful method to maintain weight loss.
The old way vs. the new way
Much of the dietary advice is aimed at helping you lose weight for a limited amount of time. This is short term thinking, which often results in the well known yo-yo effect. Eating less whilst still doing sports regularly isn't sustainable either. The body needs fuel, and preferably the good kind of fuel. Therefore, you should eat more, improve the quality of the caloric intake, and work out smarter to burn more calories and improve your metabolism. You'll see that you will slowly start losing weight.
Additionally, it has been proven that by workouts (strength training) you produce growth hormones, lower your inflammation and cholesterol levels, and improve your overall blood count so that you continuously encourage your body to burn energy. Over all, eat healthier and sufficient, do smart workouts (weight lifting), and make sure you burn more calories than you eat.