By personal rules, I mean any special restrictions you apply even though the game allows you to do more?

The few I have are:

1 - never train peasants
2 - never train bodyguard units - only use princes (but I do allow myself to RE-train them to keep up their numbers and to buff them with extra weapons and armour)
3 - never use vanilla units when my faction has something specific - eg when I play Italian factions I never train spears or sergeants, only Italian infantry; as Turks I never train vanilla archers; in VI if I have fyrdman then I don't use any other spears etc etc. The only exception I allow is if the special unit is high-tech, then I will use vanilla units until the tech is ready
4 - as a Catholic faction, only have one Grand Inquisitor

I'm sure there are more, but they're the main ones, really just to role-play and cut the cheese to a minimum So what rules do you add into the mix to spice it up a bit?