The rules we use.

There are no real 'rules' that I use to master the Atrilian campaign.

A. The referee rules
LOGIC and the WHIM of the referee are usually enough for most actions like
raising tax, building roads, troop movements, manufacturing weapons for an
army, travel, and similar actions.

B. Magic & Monsters
2nd edition AD&D rules are used for magic and monsters. Some of them are
from the Al-Qadim setting (e.g. naval rules, genies), from the PlaneScape
setting (e.g. planar travel), or from recent issues of the Dragon magazine
(e.g. Spell Paths).

C. Tactical combat
The war game 'Ancients' by 3W is used for mass combat, with several house
variants (magic, monsters, leaders).

D. Weather generation
I've written a program to generate weather for the campaign but, given the
setting, the weather's usually 'sunny'. Only the monsoon might be dangerous
for sea travel.

E. Assassination attempts
We have strict (house) rules for such attempts to ensure no one complains.

Well... that's about all. I'm working on tables for droughts/crops, yearly
tax and monthly expenses, and similar stuff, though, to make the game
funnier.