Because the writer's credibility is at stake in a persuasive essay, the essay must be well reasoned and supported with examples, expert opinions, facts, and statistics that cannot be disputed. The thesis also must be reasonable.
Now, in order to make a logical and practical argument for banning smoking on college campuses, you may need to modify the topic. After all, it is not feasible to eliminate all smoking everywhere on a college campus. Doing research on how towns and other communities have eliminated smoking in restaurants and other public buildings should provide information you need for support. While there are towns (see information on Massachusetts), it seems almost impossible to prevent people from smoking somewhere outdoors. Therefore, to make your argument stronger, you may wish to have a thesis that argues only for the elimination of smoking in any of the school buildings, the campus restaurants and cafes, the student union, and such (state whatever building you think--do not write "and such"). This argument can be supported with facts, statistics, and testimony from medical authorities on second-hand smoke.
So, try out a position statement that contains two broad, fundamental reasons for a writer's position. For instance, you could write something like
Smoking on college campuses should be banned in __________________[state which buildings] because second-hand smoke is harmful and because smoking is offensive to those who do not smoke.
Before you begin, write a pro-con table so that you can anticipate the counterarguments that your issue gives rise to and that you must refute. Definitely do much research, so that you have relaible and objective support. Organize your essay in the order of importance, beginning with the most important reason. For more assistance on writing a persuasive essay, see the link below.