I have quit, I call it quitting cause I don't buy my own, although I still have like one a month. Is a simple process. Originally I was on about 15-20 a day.
First port of call, every time you crave do some sit-ups or push ups, you can do this at work without being too much of a pillock, I did 20 for each craving, it needs to take at least 20 seconds. Exercise will take your mind off of it. If your not the sporty type I wrote some notes for my novel for 5 mins or drew some concept work for my comic these will also work.
Secondly have a scenario where you are allowed to have one, but make it strict so that it only happens once a week or so; my scenario was if I had had two pints and I was out with a friend who was also smoking I could have as many as I wanted. Do not break the deal, the best way to find a good deal is think about when smoking feels its best and only do it then, you'll appreciate each cigarette more and you'll smoke ALOT less without craving as hard.
I now don't smoke during the day or when I'm on my own, I still struggle if people around me are smoking, but I have broken the daily habit. The first 2 weeks off is hell, craving can be as bad to cause you physical pain, I used to get stomach cramps. Keep at it.Personally patches and gum don't help with the craving and just make you more aware that your not smoking. After a while you will get an awfully bad cough and your lungs will start to get rid of the crap that has been lining them (6 years of crap in my case). If you are under 25 and you quit the effects (non-carcinogenic ones any way) are completely reversable.
Finally take up a fitness regime. It helps having something that you can notice will get worse when you smoke. I took up boxing after I quit. You never crave after a hours hard exercise.
Mst importantly remember: you only CRAVE when you are BORED - occupy your mind.