I noticed a difference (lost 10 pounds) when I started walking at least 2 miles a day, or more.
the experts say 30 minutes exercise 3 times a week - that is bull-hockey and will not do a thing. I aim for 1-2 hours a day, almost every day.
Also, do not keep foods in the house that you shouldn't eat. It is a lot easier to resist temptation ONCE in the grocery store, than multiple times at home.