First, here's something for you to consider. If you've tried all kinds of diets and still have not lost much weight, it could be a matter of genetics. In this case, you really need to visit a doctor to find the best way to help you lose weight.
However, for all the rest of you, the cause of your obesity is you didn't eat healthy foods and weren't physically active. So you'll need to admit that you are responsible for the mess you are in. Understand that if you truly want to experience weight loss, you need to improve your diet.
Additionally, you must see a medical professional to confirm that you're healthy enough to start a diet. Furthermore, they would be able to advise you on proper weight loss.
It's best to go for an achievable goal so you do not become demoralized if you decide on an unrealistic one. As an example, the possibility of losing 1lb every week is likelier to happen than losing 1lb every day.
Then decide on a long term weight loss goal that you can achieve in a few months. As an example, you can a set a goal to drop about five pounds a month. You may think it's not a lot but 5 pounds in ten months is 50 pounds of fat that's gone for good! Furthermore, you would have lost weight without having to sacrifice your health.
In addition to your diet, you should do exercises for expending calories. If exercising is new to you, don't worry. Simply taking a walk is good enough for beginners, as long as you are starting to be more physically active.
After a week or two, and as your strength improves, you can walk faster or for a longer period. It will be effective if you can sustain a heart rate of 120 beats a minute for a minimum of 30 minutes.
The effectiveness of the dieting info above have been established. But they won't be effective if you don't change your attitude and actually get up and start taking whatever step is needed for you to experience weight loss.