There is no definite answer, but there are some leads. People smoke because of the way cigarettes are advertised and where they are shown. People also smoke because they believe smoking will make them act, look, and/or feel different.
Who smokes? High school graduates, blue collar workers, and men in low income brackets who are more likely to smoke than men in higher income brackets, white collar workers and people with college educations. Women who work are more likely to smoke than housewives, or women in households with a low family income. In addition, children from households where the parents and siblings smoke may learn the habit more frequently than children in smoke free homes.
Advertising techniques are one of the main reasons that people begin to smoke. Cigarette companies claim not to target young kids, but that is very untrue. Have you ever seen a billboard with normal, middle aged person smoking? Do they show people with stained teeth, wrinkled faces, and a large cloud of smoke hovering over their heads- the direct results of smoking. No. Instead they have figures like Joe Camel. Some children are as familiar with Joe Camel as they are with Mickey Mouse! In the first 4 years that the Camel ads featured Joe Camel, smokers under 18 raised from 1% to as much as 30%. The cigarette companies know that children like humor and cartoons, and Joe Camel has both.