Many times when folks want to lose weight or become healthy, the first thing they do is try to overhaul their entire life at one time. They start eating super clean (cutting out all junk food and other foods they enjoy), cut calories too low, and try to quit smoking. All of these are noble, and some even appropriate; however, doing all this at one time is a recipe for failure (at lease for the long-term).
I definitely think that quitting smoking is important, if one wants to lose weight then cutting calories(not too low) is important, and eating somewhat clean (remember balance and moderation) is important. However, what is more important is to decide what your first priority is. Your plan of action should be to implement changes in stages.
If one was looking to become “healthy,” then they could start a program to cut cigarettes. Once they have accomplished that, they can clean up their eating, and after they have accomplished that, then they can concentrate on eating for weight loss. Now the order does not really matter, and is up to the individual, but what is important is not to try to do too much or change too much at one time. Success is a process.