Here's a tip that helped me. (I have to credit my chiropractor for this one.)
It takes about 7 minutes to smoke a cigarette (I had that down to a science), but it only takes about 3 minutes for a craving to pass. So, try this, every time the thought crosses your mind. Set a timer for 7 minutes. Breathe as deeply and slowly as you can for those 7 minutes. Your craving should have subsided by then. If you can't afford 7 minutes, just set your timer for 3 minutes (I'd usually get bored by 3 minutes anyway).
You'll get some badly needed oxygen to your brain, and the deep breath feels good now that you can probably breathe a little deeper. And what have you lost? 3 minutes you would have wasted on a smoke anyway.
I'd love to hear if that's as helpful to anyone else as it was to me.