I hate to say it, but Christian is kind of right...
Each 500 fewer Calories each day than you burn. Jogging is probably the best way to do this. If you keep it up, you'll lose 1 pound of fat every week. That is a healthy way to lose weight. Other ways are simply not healthy...
Also, doing crunches and all that is going to burn very few Calories. It will, however, tone your muscles, but you cannot possibly lose fat from any particular part of your body by exercising that/those part(s). In fact, you will build muscle in those areas, and make yourself look fatter until you lose the fat itself.
You can use www.wolframalpha.com to calculate how many Calories you will burn when you run. Type in your age, gender, height, weight, and add "running" or "jogging" and the amount of time for which you ran or jogged. It will tell you how many calories you burned. For example, I'll use my information: "male 20 yrs 160 lbs 5'10" running 30 minutes." Hit "enter" and get your results.
Another thing to remember is that you cannot eat too little. If you eat too little, your body will start storing everything you do eat, and you will get fat as hell in no time. So, eat regularly, with a fair amount of protein, carbs, fruits, veggies, etc.... and just be sure you're burning 500 more Calories every day than you are eating.
I know several personal trainers, and this is what they've told me.