Numerous stories about plastic bag bans here on PBBR will give you some direction.
In the Grassroots Efforts section, read about the "Just Bag It" campaign in Hailey, Idaho. Bag It Bellingham, another successful effort resulting in a bag ban, was spearheaded by Brooks Anderson and Jill McIntyre Witt.
For a specific, step-by-step approach to starting a plastic bag ban movement in your area, there are two websites I recommend. Both sites have done an excellent job in creating the material.
Surfrider Foundation has a site called 'Rise Above Plastics' that is loaded with information and statistics about the harmful effects of plastic. Their "Rise Above Plastics Toolkit" is a phenomenal resource for anyone interested in improving the environment. The Toolkit also contains specific steps to starting a bag ban.
Plastic Pollution Coalition is another great resource for information about plastic pollution. They also publish a guide that answers the question: "How can I do this in my town?"
Go ahead. Get involved in helping the environment. Start a plastic bag ban movement in your hometown.