Which factors in weight loss and successful weight management are the most important?

Diet and exercise. Sorry. No magic/special info. The best answer is healthy low fat lower calorie diet with more interval cardio and light strength training.
Eliminate foodallerg. Hidden food allergy is the major reason for weight gain - increases inflammatory response in body, makes people Insulin insensitive, creates multiple disease process - if you get rid of food allergy or atleast heal the body any weight loss program would work.
Weight management. There are 4 majors factors;1.The most important is excellent nutrtion. You cannot lose weight without this. Focus on low glycemic index foods;2.Exercise must be regular /consistent, combination of cardiovascular and strength training;3.Hormonal imbalance correction. It is important to get your hormone levels checked;4.Use of supplements.