Follow these fool proof rules that I've totally made up as I went along and you might just make the next Fancy Pants.

• All roles purpose or lack of one should be immediately apparent before a person even joins the game.
• The path to winning must also be plainly obvious
• Keep it under 11 players but over 5, 7 is actually a magic number.
• The setup must allow a Town to lead and a Mafia to act.
• Interaction not action must be at the core of how to win in the setup.
• KEEP IT SIMPLE STUPID.
• The setup must have a majority of players responding to the actions of a just a few roles at a time.
• Make sure you're never the only player who knows the setup strategy when playing or hosting it.
• Players must have have room for a reason or an excuse to act quickly.
• A setup shouldn't look or feel like who wins or loses is based on luck, Even if it is under certain circumstances.
• Keep to exotic roles to a minimum or don't include them at all.
• Avoid excessive power roles, Players don't always want to focus on role mechanics and want to focus on player interaction.
• 3rd party roles with mechanics that aren't obvious make it incredibly hard for players follow strategy even if it's available.
• The more the players can deviate from the optimal strategy for the setup the less fun they are likely to have.
• It's gotta have a catchy or cool name, It helps if it can be abbreviated.