Best way to lose weight and keep it off?

I went on a diet last sumer and lost 18 pounds in a month, no lie but, that was the worst thing I could have done! when you lose alot of weight fast you gain it ALL back plus some, I am seeing a doctor about my weight and I go every month and weigh in and get measured, I also joined a gym. everyone will tell you, it is best to lose 1-3 pounds a week. I eat alot of soup, salads, tuna fish with fat free crackers, backed chicken, potatoes, apples... Good luck, stick with it, and dont get discouraged if at first you dont lose!