Thanks @air-clinic for this important topic of discussion. I have a genetic tendency to grow really fat and struggled with weight gain over the years. I have however learnt a few cogent things by which I now live and maintain a relatively healthy body weight that I'm comfortable with.
A healthy weight is directly proportionate to a healthy lifestyle. Hit and run diets may show fantastic results in the immediate, but in the long run, our bodies gain back the weight as soon as we relax on the diet. A healthy lifestyle is a deliberate and consistent one; i.e. one can decide to cut down on sugars, watch out for calories in foods, reduce one's intake of carbs and consciously increasing water intake.
Exercise is very important to maintain a healthy weight and it doesn't have to be rigorous although that is great for physical fitness. It can be as simple as walking 500 steps daily and getting up to stretch and squat every once in a while.