The Fallen adhere to a wartime code of ethics, so nearly anything is excusable in the name of the cause, provided it doesn't become an issue of contention leading to a breakdown of morale or unity. In those cases, the leaders of the Fallen must act, and swiftly, to maintain order. For the most part, the rules and guidelines of the infernal court are simple ones.
Obey the will of your superiors:
The infernal court is built on a feudal hierarchy, and demons are expected to respect and obey the chains of command. Failure to do so may result in punishment. Of course, the ruling ranks are expected not to abuse their powers or authority, or else -their- superiors may punish them.
Respect the territory of others:
Demons are expected to respect the domains of other fallen, and not to interfere with things like another demon's thralls. This rule prevents all-out conflicts between the fallen within the courts, but is honored more in the breach, as demons strive for control of territory and mortal pawns. Such conflicts are usually subtle, except in cases where a demon has little fear of punishment or the tacit approval of a superior to dispose of a rival as he sees fit. For example, an upstart lord with the support of the local overlord or baron does not need to respect the territorial claims of others in his domain, since they are by definition defying his rightful authority.
Protect the security of the infernal court:
The fallen have many enemies, and they hold to the wartime standard that cooperation with the enemy is treason. Whatever their individual agendas or conflicts, the fallen are expected to safeguard the infernal courts and their fellow demons from the various threats awaiting them in the mortal world. This includes demon-hunters, servants of the Earthbound, and other potential dangers. It also means the fallen should not do anything that could cause the masses of humanity to unite against the courts. Thus a measure of subtlety and discretion is required in the court's dealings with mortals.