I think different things work for different people. For me, someone told my 4 year old that if I kept smoking I was going to die and so the next time she saw me light up, she grabbed my leg and cried her little heart out that she didn't want me to die. It was a little dramatic but I felt so small right then and there and so selfish that I was hurting my body for a few moments of pleasure and here my baby needs her momma to be healthy and strong for her.
So I decided right then and there to stop and I just did. I still get tempted every now and then and I have taken a hand full of puffs since that day 7 years ago, but being here and healthy for my babies was motivation for me. My husband....that's not enough for him and he has tried quitting several times and hasn't managed yet. I think each person just has to find the strongest most motivating reason for them to quit and that will keep them going.
Most important I think is when people try quitting and they slip up and smoke, they just think "well I already screwed up today, I'll start over tomorrow" and then the screw up the next day so it's a cycle that doesn't quit lol. If you mess up and smoke, just say...you know what that's ok. I WON'T smoke the next one. The next urge that comes around...follow through. It's a day by day, sometimes even hour by hour self determination. And you always keep your motivator in your mind so you have the strength to put it down.
My best advice. It's lame but it's all I got