Crash dieting is a complete NO. You don't keep the weight off once you stop, because you're not sticking to the "bad" habits you've created for yourself. Losing too much weight in a short amount of time can lead to heart problems, skin problems, digestion irregularities, and etc. So you should only lose a few lbs a week.
Exercise is a must for losing weight and keeping it off. You can't do it with a healthier diet, even though one does need to cut down on fried foods, Trans fats are terrible stay completely away from those. If you have a sweat tooth or a thing for junk food go with things that are Unsaturated. Cereals are good for this, since they are sweet and filling - if you can't do the Fruit thing. Banana's with my Cheerios as a snack in the middle of the day is what I go for instead of cookies.. lol.
Also, REWARD yourself... if you have a weakness for food, don't reward yourself with food.. but if you've hit a goal.. like say.. losing three lbs.. or dropping all Soda consumption, reward yourself with something so at least you know its worth it.. lol. Some people don't stick to diets because they don't know when the "fun starts" during their changes.