I started smoking when I was 15. Smoked for a good 3 years. Let me tell you one thing, those people that say "oh this is my last box" or last cigarette, will not quit at that attempt. I just didn't smoke one weekend because I was busy with family shit and after that I thought hey what's the point, and I just stopped. It has been 4 years since I smoked.
If you want to quit, throw the box away right now, and never turn back, no thinking just do it.