Teach that everything you see, hear, and eat affects how we act. Talk about how each item will affect the doll as you place the items in her head. Bad pictures teach us that bad things are acceptable. Bad music might make us angry. Cigarettes can hurt the bodies Heavenly Father gave us and enslave us, etc. Dump out the bad stuff from Raggedy Ann's head. Allow the class to throw the bad things in the trash can. Teach that the difference between you and Raggedy Ann is that when bad things enter your head, they don't come out, except through the Atonement. It's very important to make sure we don't allow bad things to enter our minds. Commit the class to making good choices.
This object lesson was told to me at a presentation by Joann Hamilton (http://www.StrengthenTheFamily.net/) as a lesson for teaching children the importance of avoiding pornography specifically, though it has application for the Word of Wisdom also.