I had my last cigarette in the middle of March, after smoking for the last 18 years. Since then, numerous friends who also want to quit have asked me how I did it. Unfortunately, I haven't the slightest clue.
I didn't read a book on how to quit, although I know that's worked for some. I didn't use any nicotine-replacement strategies. No prescription drugs either. In fact, previous attempts using some of those methods were complete failures.
Cold turkey worked for me. I'm not trying to boast about my willpower - if I had any, I would have quit a long time ago. It's the horror of withdrawal that keeps me away from temptation now. I definitely don't want to experience that ever again.
As with everything difficult in life, practice makes perfect. I learned from every attempt at quitting, and those failures helped diminish my fear that withdrawal would never end. Kicking nicotine is scary, but the fear is even worse. You convince yourself that it's never going to get better, but it does, and sooner than you think.
The biggest danger for me is letting the monkey on my back talk me into believing that just a little taste wouldn't hurt. It's amazing how quickly just one drag turns into one cigarette, which turns into a pack and then a complete relapse. I've gone through those steps in less than an hour after being off nicotine for several weeks.
Withdrawal is horrifying and humiliating, but it gets better. Once you get past the initial hump of steadily increasing discomfort, every day is slightly easier than the one before. Improvement seems almost imperceptible, but you can still feel it happening. Clinging to that feeling kept me sane the first few weeks.
Mostly what I've learned, though, is that there's no single solution that fits every addict (let alone every drug). In the end, it was a spur-of-the-moment decision that led me to quit: I ran out one day and decided to see how long I could last before buying another pack.
For me, turning it into a game rather than something with a lot of commitment attached to it was what worked. Your mileage may vary.