No Snacks, no sweets, no seconds. Except on Days that start with S. Too simple for you? Simple is why it works. Look here for questions, introductions, support, success stories.
A Documentary called How to Live to a Hundred, from the BBC in the UK.
Watch at around 11:15; the lady (105 years old) claims that she likes a treat, eats toast for breakfast, but "rarely" eats outside of her three meals.