Unfortunately, you can't stop people from smoking. It's their own choice. You can try to persuade them from smoking, but that's pretty much it. Like I said, it's their own choice that they're responsible for.
You can't really tell them to stop, but tell them to think about what it is doing to them on the inside. People die alot sooner if the smoke, they have a great risk of cancer, and a lot more unhealthy side effects. Hopefully the person will stop.
I'm sorry it's an individual disition .As long as its legal .Really what can we do ?We can let the smokers know how dangerous it is for them and others .But as far as that goes people will just continue to die horrible deaths from smoking.