Below is a link to a targeting poster that we have created to help select the proper targets when creating rules and monitors. The poster illustrates some of the most common scenarios and provides best practices on how to properly target rules and monitors. Feedback is always welcome of course.

http://download.microsoft.com/download/f/a/7/fa73e146-ab8a-4002-9311-bfe69a570d28/BestPractices_Rule_Monitor_REV_110607.pdf