One of the best ways to create your own policy is to contact other organizations that may have done this. It is fairly easy to adapt someone else's policy to your situation. However you go about it, your policy should be relatively short, not require huge amounts of paperwork, and be unambiguous. Don't develop a policy of this sort without extensive consultation with front line staff. You would think it would be fairly clear that simply creating a policy regarding violence in the workplace is not sufficient and that each employee needs to understand it.
Communication is obviously important.
My experience is that a good number of organizations that develop excellent policies on the subject fall short when it comes to communication. Even in organizations that have had such policies in place for several years, I find a good number of people who don't know what the policy means, or have found that when they follow the policy, they get hassled by management. The policy stated that when an employee felt a potential for physical harm, they were to hit their panic button, and this would summon additional personnel or security. Unfortunately, the manager of the installation made it clear that staff were NOT to follow this policy unless the threat was immediate and obvious. Not surprisingly, staff were confused and angry about the manager's clear violation of corporate policy.