Welcome to the forum. Smoking
is bad for health, it slowly destroys the lungs and makes life miserable. To quit smoking is a good idea but the determination taken should be strong. It will be better to chalk out a daily activity routine for your friend.
He can get a crave to smoke at times, he should strictly engage himself in other activities like enjoy doing workouts under an expert guidance, he can take some of his favourite snacks instead of a cigarette whenever he gets an urge to smoke, he can munch on nuts, he should take his favourite juice, soups and water to keep hydrating himself.
He should engage himself in activities like games, sports, concerts, movies, etc. The more busy he is the better is his performance. He should reward himself for not smoking. It is important to help him take nutritious diet. Good sleep is equally important. He can visit a counselor for help and assistance. Take care.