It's true, the only letters I've sent my congressman are form letters.
I should make them ambivalent too:
Dear Congressman So-and-So,
Thank you for attending legal sessions to represent me. I appreciate seeing you on C-SPAN.
During the upcoming session, several issues are slated for debate which I care deeply about. When the time comes, I trust that you will give serious thought to these issues, carefully consider the circumstances and ultimately make a choice that's in the best interest of our nation.
Again, thank you for your representation, and be assured I will keep in touch.
Sincerely, Loyal Voter