Things to avoid
1. Too many power roles
There are three reasons this is a problem.
Firstly the game becomes more about the power roles in play, and vanilla players can find themselves effectively acting like a cheerleading squad rather than active and valued participants.
Secondly each power role you add has not only their power, but also the sometimes overlooked property of being able to avoid a lynch via claiming. In this respect, every time you add a unique named player you need to consider them as a town special with that “immune to lynch” skill.
Thirdly, it’s harder to balance the game the more power roles you add. Particularly given the second issue, it’s very easy to unbalance the game in favor of town via too many power roles. This is particularly noticeable in the late game when it can easily turn into a case of “let’s just lynch all the players who haven’t claimed a distinct name/role and we win” for town. To be fair, scum can sometimes slide through this hazard with a well constructed fake claim.
2. Not doing the maths
You should really run through the game a few times to see how it is likely to pan out. Try with random choices, try it with a lucky choice for one side or the other etc, or with each side making the best choices and see if the game is easily swung irrecoverably one way or the other, or simply unwinnable for one side or the other. Try to work out if common cheesy tactics like mass role claims will break the game.
3. Adding people late
You’ve recruited players, designed roles, sent out the role PMs and now one of your favorite players asks if you’ll let them join the game. Don’t do it. If you’ve balanced it right then their addition will unbalance things, and generally if someone is added late they’re given vanilla town since that tends to be the least damaging choice to balance … but then it upsets things because that is obvious so they’re really a ‘mostly-cleared vanilla town’ rather than ‘vanilla town’. Besides, you may need a replacement player after the game starts and having someone who wants to join the game can make replacement much easier.
4. Decide your night move order in advance
Pick a way to order night moves and stick to it. If you end up with conflicting moves and haven’t thought about this in advance then you’re suddenly open to temptation to try and balance things up a bit or favour someone unfairly. If you’re not sure how to order your night actions, Natural Action Resolution is a good process to use. Google it!
5. Make sure you have enough time
If you’re rushed it’s easy to make mistakes. Vote counts are the obvious ones, but missing someone’s PM changing their night action, or goofing up your night action resolutions can lead to an unfair game for the the affected team.
6. Avoid designing roles with a percentage chance of success.
The entire outcome of the game can then hinge on a dice roll rather than player choices. That tends to lead to unhappy players.
Bottom line, you want the game to be about the general vanilla players trying to read each other’s play. That’s the bedrock of the gameplay, and if you get caught up in too many fancy schemes you can lose track of that.