My best advice has to do with how you view the process of quitting. For a long time when I'd try to quit I'd go a few days or even a week, and then I'd break down and have one at which point I would think "I have failed" and the psychological impact would spiral me into full on smoking within a day or so. It was only when I started looking at quiting as a "moment by moment" sort of thing that I was able to stop. Every moment that I didn't have one was a small victory in and of itself, and so If I had a cig it wasn't a sort of "ending my streak" but simply one moment when I succumbed to a human failing, and as such I would think "So what, I had one cigarette in th past three days, I'm still doing real good." It kept those moments when I broke down from dominating the process.
At any given moment the battle is not "To Quit Smoking Forever!" the battle is to simply not have a cigarette right now.
Hope it helps, Good luck