This is a great question in view of the health benefits alone. There are several things you can do from a behavior modification point of view to help someone stop smoking.
First, many people who want to stop smoking have a difficult, because there is an impulse simply to put something in their mouths. Hence, a good behavioral technique is to replace that impulse to put a cigarette in their mouth with something else, like snacks. And if you can have that snack be healthy, it would be even better. So, the idea is to replace one desires with something new.
Second, exercise can also help. If you get your heart rate up and get your blood circulating, this can help with the craving for nicotine. Moreover exercise, in general, will help with feeling good naturally. This alone can help tremendously.
Third, if a person just needs to do something with their hand to keep them occupied. They can download some games on their cell phone or do something similar. Again the idea is to replace one habit with another.