How To - Tips for Various Actions
How to Address a Letter to a Government Official. This is a general 'how to' site that addresses the formal aspects of such a letter.
Write Your Elected Officials. From the Christian Coalition, this includes less info than the above about the formalities, and more about letter content. If you want one-stop shopping for letter writing, this is it.
Therefore, since I myself have carefully investigated everything from the beginning, it seemed good also to me to write an orderly account for you, most excellent Theophilus, so that you may know the certainty of the things you have been taught. Luke 1:3-4 (NIV)