The argument over negative calorie foods is going to continue on rage on, but there's one thing that absolutely can not be argued with: a diet that is very high in the fruit and vegetables on this list is going to help the far majority of people lose weight, and possibly lose weight very quickly. For many dieters who have had bad eating habits for a very long time, it's surprising how much weight is lost just from stopping bad habits: soda (which the carbonation also keeps on bloat and excess water weight), sugars, and fast food are are very bad for a person's health, and for many people just cutting these out and doing nothing else is enough to lose weight.
Now snack constantly on negative calorie fruits & vegetables all day like cucumbers, carrotts, apples, grapefruit, and watermelon and not only are you constantly eating, which keeps the metabolism burning, but you're not feeding yourself any fat and you're not feeding yourself a lot of calories: meaning you're getting full on 200 calories instead of 800. Whether or not negative calorie foods technically create a negative caloric effect or not doesn't really matter because the point is that these foods are extremely healthy, low in calories, but also high in vitamins and fiber that you need to be healthy and full.
So one of the best diet tips would be to tell people to eat more of the foods that are on a negative calorie foods list. In addition, this is obviously a very vegan friendly diet and a good boost for vegetarians, as well.
However this diet isn't for everyone, and if this information just isn't quite what you're looking for, then take a look at this site that has a ton of good information on how to lose weight.