Find your BMR, and get that amount of calories. Maybe a little more at the beginning.
Most people are probably going insane right now thinking why would I suggest the BMR amount of calories. Well good people, I will tell you why. The BMR (Basal Metabolic Rate) is the amount of calories your body naturally burns. It doesn't include any movement or other uses of calories. I assume that since you want to lose weight you're running like crazy? Stop doing that. It does burn calories, it does get your metabolism going, which is why I recommend doing a bit of running every day.
But the main things i recommend for the maximum weight loss is:
1. Do a fast walk/jog every morning for at least half an hour. Fast in this case doesn't mean the speed at which you are running. It means, as soon as you wake up, grab a drink, and get walking/jogging. go a comfortable pace but not too comfortable. What this does is essentially... Your body has no food in it right? What happens when your body has no food energy to burn and you're doing activity? It burns calories that your body has already stored up. Also known as, fat. When you get back from this, eat a good, healthy breakfast. Stay away from simple carbs such as white bread, table sugar, potatoes. Potatoes are okay sometimes, but it's a simple carb which increases the chance of you gaining fat.
2. Lift light weights for high reps. Pick a weight that you can lift for about 20-30 reps. Do a variety of exercises and switch it up everyday. Never target the same body part twice in a row. You aren't going to pack on serious muscle doing this, but you will incinerate the fat and tone muscles. In my opinion, lifting light weighs for high reps is better than running because it really cranks up that metabolism as energy is used trying to restore the muscle tissue that you break down by working out.
3. Use a calorie counting app to make sure you're getting around your BMR of calories. Maybe more if that's not nearly enough for you. Losing/gaining weight is a simple equation:
Calorie Intake > Calories burnt = Weight gain (in form of fat, or if you're working out, muscle.)
Calorie Intake = Calories burnt = Weight maintains
Calorie Intake < Calories burnt = Weight loss (as your body needs the energy that you aren't taking in so it turns to fat cells to get that energy.)
Calories Burnt = Basal Metabolic Weight + Calories burnt from activities.
Use this to find your BMR:
http://www.bodybuilding.com/fun/bmr_calculator.htm
A good iPhone/Android app to count calories and nutrients is MyFitnessPal.
If you do everything I said here, I promise, you will lose lots of weight.
I helped a few friends out with their weight problems and one girl lost about 3-4 pounds a week!
You will lose quite a bit at the beginning, and it will be hard, but if you ever have a lack of motivation, think of you in the best shape of your life.
P.S. Don't try to lose 7 pounds a week long term... It's dangerous and your body won't be able to adapt quick enough.
Good luck!
If you have any further questions, quote me.