A calorie deficit must be created through exercise and a small calorie reduction. This means more energy goes out than comes in. If it were only so simple!
Appetite seems to increase with activity level (therefore cancels out energy expended), this may not always happen.
The body will attempt to conserve weight during times of increased activity and reduced calorie intake (body becomes more efficient with energy).
Scales do not tell how much of the body weight is muscle, fat, OR water.
We all know someone who eats a lot (and eats a lot of "forbidden foods") BUT does not seem to gain a pound, while others eat very little and still have difficulty in altering their body composition.
You must use weight training to build muscle mass and increase metabolism and you must exercise consistently. The energy expenditure will help develop a negative caloric balance.
Base your success on how you feel, how your clothes fit, and how well you perform in your sport/activity, NOT on how the scale reads.
Do not starve yourself. The body may shut down its metabolism and it becomes extremely efficient in saving/storing energy. Eat nutritious meals spaced evenly throughout the day to maintain the metabolism and provide energy for exercise. Reduce any unnecessary food intake.
Remember you are trying to eat fewer calories then are needed to maintain weight. Aim to reduce the calories by a maximum of 20% (i.e. 200-400 per day), BUT/ never go lower than 1500 total daily calories. Reducing the amount of fat in your diet greatly helps in reaching a calorie deficit (because each gram of fat has 9 calories).
Do NOT eat "fat-free" foods in excess. Remember the aim is a calorie deficit! There are no magic OR forbidden foods. Some are better than others BUT very few items need to be fully excluded from a diet. Allow yourself at least the occasional treat.
Choose water as your low-calorie fluid source, unless you need the nutrients that are provided by a glass of milk OR juice.
Be honest #1
Do you really need to lose weight? Losing weight often involves certain sacrifices, so determine if it is really necessary for health or performance and then make full commitment to the goal.
Be honest #2
Can you decrease your food intake without your health suffering? Try to reduce calories with your health in mind by reducing the foods with least nutritional value (i.e. processed foods, sugary drinks, excess sauces, and sugar).
Be honest #3
Are you truly hungry when you eat? Are you just thirsty, bored, stressed?
Be honest #4
Are you active for only 30minutes (your exercise session) and then stuck in a chair for the rest of the day? Consider this before you justify an increase in caloric intake.