I agree with the first answer. Don't say 'I'm never having another cigarette' that's too difficult to do and if you have one, you've ruined the whole thing so can easily just give up trying. As well as the 'not before 8:00' etc ruling , you could add in throughout the day that you're allowed to have a cigarette any time you want one, it's just you have to wait another five minutes before you light up. Look at the clock, get on with whatever you are doing and after 5 minutes if you still want one, have one. Do that every time you want a cigarette for two or three days, then increase the time delay to ten minutes, then fifteen minutes etc. If you don't stop, at least you gradually cut down.
The main factor in success , though, is having a good enough reason for you to stop. Only the person themselves will know what this reason is, so preaching to them about how unhealthy, smelly, antisocial etc smoking is will be no use. They have to come to this reason themselves.
Good Luck. It ain't easy to stop.