Flowchart? Here's what I use, in general
Q: Is he/she of noble blood?
N: Refer to as Freeman or without title for outlaws/lackeys
Q: Does he/she have a Lordly estate?
N: Sir or Lady will do. I use Dame only for unfamiliar people. No difference between knights with or without estates (~Imperial Knights)
Y: Lord or Lady. If a Lord yourself and of lower esteem (Viscount or Count), use more appriopriate title if appliccable, e.g. Margrave/Earl/Count.
If you are of higher standing (Ruler, Duke of Councillor) always use Lord. They are beneath your standing, their quarrels/ranking do not concern you.
Q: Is he/she a Duke or Duchess?
A: Use Your Grace in private conversation/letters, Duke in public messaging. Depends on relationship (I feel Duke is less personal)
Q: Councillor?
A: Use council title in the context of the relevant position. E.g. General when discussing military matters, Banker for food/economy.
Also on formal occasions, and in the eyes of their peers
Q: Ruler?
A: Unless personal, use correct title in heading, Y.M. in text. First time adressing, use the surname and realm, e.g. King Kepler of Keplerstan
Basically, if you address someone higher in the chain, make clear that you understand the exact position of your contact to avoid insulting them. If you address someone beneath your standing, it's of less importance as long as you are formally right.
One thing that always bothers me, though, are the suffixes characters bear even after they have lost a position. For instance 'Kepler Dolohov (Duke), Knight of Keplerville'. I try to decide on the context there. I wouldn't use Your Grace for (foreign)ex-Dukes, but I would use Lord, even if they have no Lordly estate. Royal Lord sometimes for ex-Rulers.
Does this make any sense? Of course many of this is highly dependant on the realm you play in.
Also: equally interesting is the way you end a letter. I've always liked Vellos' "Pleasant days and pleasant nights" (or something? tried looking it up, but I don't have any letters left). I always find it rude not to have anything between the signature and the body of text, certainly for foreign rulers. I can't imagine they simply sent tweets to each other like that - certainly not on Dwi
Though I have sinned against this principle myself.
