Try the 4Ds

 Delay acting on the urge to smoke. Don't open a pack or light a cigarette. After a few minutes, the urge to smoke will weaken, especially if you do the following:

 Deep breathe. Take a long slow breath in, and slowly out again. Repeat three times.

 Drink water. Sip it slowly, holding it in your mouth a little longer to savour the taste.

 Do something else. Take your mind off smoking by taking action - put on some music, go for a walk or ring a friend.