My grandfather passed away when my father was a teenager. According to my father, my grandfather smoked a couple of packs a day. At the time, it was not only the norm, it was encouraged. Doctors recommended that their patients smoke as a way to relieve stress. While other factors no doubt played a role, I place the blame for my grandfather's sudden and deadly heart attack directly on his smoking, which we now know is not only linked to heart disease, but that tobacco companies knew of the link even while promoting cigarettes as a healthy choice.
My grandmother started smoking when she was twelve. While I remember seeing her smoke when I was younger, as we got older she smoked in front of us less and less frequently. Her smoking affected her lungs. Although she outlived my grandfather by about four decades, her greatly diminished health was directly tied to her smoking habit. She said that she would have quit sooner (or have never started) had she known how miserable her health would become.
While I have held to a vow of not using any mentally affecting drug as I do not want to become reliant on an outside source for my internal feelings, I do not think that I would have ever taken up smoking. My grandparents' deaths illustrate two of the most common dooms that await people who choose to smoke: an early death that deprives your loved ones of having you around, and a longer life where you spend decades struggling for breath.
Don't smoke.