Breaking a habit can be simple - you just create a new one and then practice it again and again. If you've smoked for any period of time then you have probably practiced the smoking habit thousands of times. Every time you think about it, you practice it and cement it in further. Ironically, when you try to not think about it you also practice thinking about it. To understand what we mean, try not thinking of a giant pink elephant. Impossible, isn't it?
Every time you start to think about smoking just revert to thinking about something else - the positive benefits of stopping, health, happiness, being in control, smelling fresh and clean etc. If you notice a dark thought, turn it into a bright one.
For further ideas and advice and ways to stop smoking, visit the substantial resources section of this site - Stop Smoking Resources