Other than encouragement, there is little or nothing you can do to help someone else quit smoking.
The best advice you can give to help make the person who is trying to stop smoking is to tell them to not think of themselves as "trying to quit smoking", but rather to refer to themselves as "I don't smoke" or "I am a non smoker". This gives the person a positive, self affirmation as to intent, and it is positive and uplifting to refer to one's self as already reaching their goal; If that is their true goal, then they will already have achieved it.
The physical cravings will abate within a couple of weeks, but that should never deter that person from having already reached their goal to becoming a non smoker. .
I smoked for 40 years, (as i coughed, hacked and wheezed throughout each and every day and night) and one day i thought to myself: this is really a stupid and unhealthy habit, so i crushed the remaining cigs in the pack and threw them away, and from that day on, i considered myself a non-smoker.
The physical withdrawal was hard at times for the first month, but i have never known anyone to die from lack of cigarette smoke and have not had one day of regret since i threw those cigs in the trash and i am healthier now than when i smoked.