A good mental trick to try when you finally quit is to immediately think of yourself as a non-smoker. Even if it's only been a few hours or days since your final cigarette, think of yourself as a non-smoker - as if you've never had a cigarette. Then, whenever you find yourself craving a cigarette say to yourself "why would I want a cigarette? I don't smoke."
It's important that you take mental steps like this when you quit smoking. Although the physical component of a cigarette addiction can be hard to overcome, especially if you have been smoking for a long time, the physical element of your addiction is also the part most easily treated with medication. It is with the mental or psychological component of your addiction that the fiercest battle will be fought.
By thinking of yourself as a non-smoker instantly, you are taking an important, active step. Although it may seem silly to think of yourself this way if you've only stopped smoking for a day or to, try it: you'll find that if you define yourself as a non-smoker, the idea of having a cigarette will require a long justification. It will make you truly think about having a cigarette - after all: it's not normal for a non-smoker to smoke, is it?
If you fail to do this, it will simply be too easy to lapse back into occasional smoking. It is, of course, fairly common for a very recent ex-smoker to take a drag now and then, isn't it? If you don't think of yourself as an ex-smoker you'll allow yourself these indulgences - an occasional drag, or even a full cigarette now and then - that will almost certainly ensure that your attempt to quit smoking ends in failure.