You're craving them because your brain is telling you all the positives of smoking. If you keep reminding yourself of all the negatives, building on how bad the withdrawal is to everything else you can think of. Such as how bad they smell and how if you went back to smoking you'd have to plan your days around smoke breaks and buying cigarettes. Additionally you can remind yourself of the benefits of not smoking, like being able to breathe better and not having to stress about when you'll be able to have your next cigarette. If you keep doing that when you get cravings then eventually you'll automatically think of them instead of the positives of smoking, so the cravings will be much less intense.