Well, people go consult their doctor first, before they began trying any diet. Or people pick something they see on TV, and decide to try it out.
The only thing is not every diet works for everyone, because a person's body works in different ways. Some people have a fast metabolism, while some people don't have that.
So, there are two key factors in diets.
One is to make sure you eat healthy by eating three balanced meals. You have to eat food that will make you lose the weight. Eating lots of fruit is a good thing, drinking a glass of water can help you lose the weight off, and other healthy foods are a good way to keep the weight off.
Two is make sure you exercise. You can't lose weight without exercising. You must do exercise about three times a day to get the weight off. Find an exercise routine that will work for you, and that you will stick to. Do not start off with a difficult exercise routine, because you have not advanced to doing that yet.
It is important to start off with an easy exercise routine, and then work until you're comfortable doing the next level.