This is a brief video demonstrating how to tune a DLP policy. In this video, you will see three approaches to tune.
Below you will find some useful links that were used in tuning the Credit Card DI.
Regex test page: http://rubular.com/
List of Issuer Identification Numbers: http://en.wikipedia.org/wiki/List_of_Issuer_Identification_Numbers
Site for generating test Credit Card numbers: http://www.getcreditcardnumbers.com/