If you quit cold turkey I'd suggest a not trying to do it by substituting an alternative. Unless it's drinking water like Trev said. What i mean by that is, some people would chew a stick of gum instead when it was time to have a cigarette, some ate a carrot stick, some people did something else. While it's good in theory and healthy in the short term, the problem with quitting is as behavioral as it is addictive. So while at first you'll drink a glass of water instead of the cigarette, that will be fine, but the behavior will be the same and it will be easier to relapse back without breaking it. So remember, it's as important to change your patterns and behaviors when trying to quick. Change up your schedule as much as possible. If you leave for work at the same time every day, try to car pool with someone who doesn't smoke. If you have one at lunch break, try to bring your lunch so you don't leave the building. if you have one on the ride home, try to stop at the gym instead or something like that. If you change the patterns of the things you associate with cigarettes and urges, you'll have an easier chance of breaking the habit.
I believe they say you only have to do something the same way 20 times in a row to make it a habit. That might just be for seatbelts though, haha.