Short answer is YES, you can technically create any kind of code of conduct/rules of employment that you want. The only issue is that it must be a uniform policy that applies to ALL employees, and it must be enforced evenly. No favoritism. You just can't discriminate against pregnant women, religion, ethnicity, race, etc, but you can let it be known in the Employee Handbook that you have a smoke-free workplace, require certain standards, blah blah. You must give this to them from DAY ONE, and enforce it.
All states are pretty much "At-Will" states -- which means that you can fire anyone for any reason (outside of the protected classes). So make your rules IN WRITING (so they can't get unemployment benefits), distribute it to ALL employees, and if they don't like it they can quit.