I was always an off-again-on-again smoker. Never had any difficulty quitting for a few months to a year, once I truly made up my mind to do so. Unfortunately, it was just as easy to start back up again. Such a nice, relaxing little thing to do... Too bad it can kill you.
Anyway, I've finally given up the habit altogether. It's been about a year-and-a-half now, and I have no desire to start up again. And I did it this time like I've always done it--cold turkey.
I realized when I hit my mid-thirties that I truly am not invincible (gasp!) and that all the little unhealthy--albeit pleasurable--choices I make in my life come with a price. For example, I started noticing in recent years that it takes a good couple of days or so for me to recover completely from a full night of drinking, a pack or more of cigarettes, and a 3:30 a.m. bed time. In my twenties, a few nights of such behavior barely phased me.
I also have cut my beer intake tremendously, and I rarely partake of the "green tobacco" these days. For me, it's just common sense. I was never addicted to any of these substances. They were just bad habits in my life, like biting your fingernails or something. Once I could actually feel some of the longer term effects on my body as a result of these habits I quit.
I also was motivated to quit as a result of becoming a father. The image of my kids standing at my casket before they hit high school (yes, I have an active and morbid imagination) is a cold bucket of water over the head that helps me to make more responsible decisions in terms of my health and finances and what have you. Sure, I still could be hit by a bus stepping off the curb, but to keep hitting myself with a bus, metaphorically speaking, night in, night out, would be foolish. Simple as that.
Anyway, that's my story. Good luck with your own struggle.
Matt