This is going to be the most difficult. As usual, all the buttons need explanations, the interactions at different diplomacy levels need explaining, new treaty system should be discussed, relationship between Ruler and Dukes/Council/Lords/Knights in different systems should be discussed, and please try to avoid this turning into another argument about button power vs influence.
Though I know most of the mechanics, I'll leave this one to someone who has experience being ruler. *looks at Matt, Vellos, and Tim* 8)