The best resource I've found for preventive action is any action taken in response to trends. In effect, you're responding to an issue before it becomes a big problem.
There are any number of ways to tackle the documentation. Preventive action could be picked up in project type documentation, using action plans and activity reports (similar to continuous improvement). I've also used the same form as corrective action in dealing with smaller companies...just use the "long term action" section to reference the project plan or Gantt chart, and keep the action open provided monthly "progress reports" become part of the CA/PA record.