I smoked for about five years and then made the even dumber decision to use smokeless tobacco for about five years after that. I tried to quit several times, but finally did it for good in 2005. Here's what made the difference for me:
1. I got really ticked off that I wasn't in control. I had voluntarily given control to some tobacco company that designed a product specifically to get me hooked and then profit from my addiction. This made me really mad.
2. I decided that quitting was the most important thing in my life. This allowed me to be lazy, unproductive, unsocial, and a jerk to my friends and family when I needed to be. As I write this, it sounds odd, but to quit I needed to be very selfish. In previous quit attempts I always find some excuse to go back to it and the excuse usually revolved around other people - something like "I really need to get this project done and I can't concentrate, so I better go get a smoke." Only when I was willing to let other things slip while I focused on myself was I able to finally quit.
3. I found a good online community of people quitting. I became a member of the forum, visited daily, and participated. The one I used was quitsmokeless.com, but I am sure there are similar sites for smoking.
4. I improved my diet. I realized that many of the signals that I was interpreting as nicotine cravings were actually signs of hunger.
5. I used nicotine gum for the first six weeks or so, tapering off it during that time.
6. I realized that it was one of the hardest things I would ever do in my life. Previously I thought "I'm a smart, disciplined person, quitting should be easy." And then when it got hard I would doubt myself and cave. Only when I accepted quitting as the challenge it truly is was I able to summon the determination to get through it.
Good luck with your quit. And when you are successful (and you will be sooner or later) you'll find that the health benefits are only outweighed by the personal growth you'll do in the process.