http://b12patch.com/blog/smoking-and-vitamin-b12-deficiency/
The way I did this was by making it a bit harder/uncomfortable to get my cigarettes, and by tring to smoke just 1 cig less every period.
E.g. I would usually carry around a pack in my jeans, so I started leaving them at the car, so if I wanted to smoke it would be harder for me, so that would reduce the impulse when I was very busy or just didn't have the time. After some time doing that it was no longer a problem so I had to up the ante: I would only bring so many cigarettes with me and leave the rest at home. So if I knew I only had say 10, I would try to spread them over my working hours.
Then I would bring only 5 and so on. At some point, some 2 years later I would only smoke 1 in the mid-morning, 1 after lunch and 1 in the afternoon.
Then I would set myself to only have 1 after lunch. Then 1 every other day.
After that it was easier to go several days without smoking until one day I just didn't feel like buying more and I stopped.
Also, I think what worked quite good for me was to avoid "punishing" myself if for some reason I didn't make it one week and smoked a couple more, as long as I was kept reducing it overall the other weeks.
Doing it like this was easier for me I believe, because my own body was breaking the addiction so I just enjoyed smoking less and less, which I think it's why I couldn't do it cold turkey: my craving was stronger than my will. However reducing the craving over a long period allowed me to weaken that craving until my will to stop was stronger.
I know my method sounds a bit stupid if you phrase it like "how to quit smoking in 3 years", because everyone wants to do it NOW. But by avoiding such an unreachable (to me) goal, I managed to quit even if it took that long, so I am happy with the results :)
Hooe that helps.
Also for him he did the "don't break the chain" method. Bought a paper calendar, a pen, and a red and green marker. Week one was 8 cigarettes per day, week 2 was 7 cigarettes per day, etc. You write down that number with the black pen through the calendar so you know what your goal is. Exception being for 2 weeks you do 2 cigarettes per day, and for 3 weeks you do 1 cigarette per day because when it's that low you are fighting more of the mental aspect.
Then every day at the end of the day, exactly midnight you can put a a big green checkmark if you kept to the number, or a big red X if you didn't.
The idea is that you never want to break that chain of green checkmarks.
He hasn't smoked in a few years now. :)