What should you do to lose weight if you are 100 pounds overweight?

A friend of mine in 5'10". A year ago he weighed 330 lbs. He now weighs 220 lbs. He said that a huge key to his weight loss was learning that most of the time when he felt hungry, he was actually thirsty. So when he felt hungry he would drink 16 oz. of water. Then if he was still hungry after 30 minutes he would eat some food. He also ate smaller portions and rode his bicycle and so it was a combination of things, but he claims drinking water when he felt hungry was a major factor.