For one, make a guild, or find a guild with that theme in mind.
For another, watch the Godfather, or read up on how the Mafia and other criminal organizations act and operate. Depending on which, you'll have different specific moral codes, but generally for a criminal organization, a big one is an almost zealous loyalty to the organization. That's a big one. For the Amero-Italian Mafia, they're effectively one giant family, so that's always a very big part of their identity too. Legal corporations try and do the same (inspire feelings of loyalty and family), but it's more mixed in its reception.