Design phase
In general it's a good idea to design in advance with role allotments for each number of anticipated players, probably 12-18, discussed more in ‘game balance’ section. First one has to decide whether or not to use clues, events, etc. Clues in particular help spice up otherwise boring Day 1’s and add a layer of deduction to the game that players tend to respond well to. Biggest concern is always post slumping, which clues tend to help avoid, however they have the drawback of potential being ruinous to the game if they are too simple, ignored if too hard, and damaging future games if red herrings. Clues are probably best done detective-style, as opposed to complex riddles or such, aiming for something akin to the standard logic problem, for instance, a fixed group of traits everyone has (hair and eye color, weapons, clothing, etc) each with its own sub-groups (red, blonde, brown, black hair) and a few initial clues around the day zero victim, if you have one, with release on a random basis or off lynches and actions.

Complexity – More theme is more interesting but also leaves a lot of room for accidental game breakers, and idle comment in a RM like ‘Player X gives you a wolfish grin’ can be a big accidental give away to a werewolf role, but also is very likely to be interpreted as that by players, the latter is fine, good even, the former can mess things up. Any given example of this will seem very obvious but moderators often make them anyway.

Goals – Goals can be used in conjunction with clues or by themselves to stimulate posting. General a carrot is better than a stick, but as an example…. “Player X, you are smooth talker, and have a double vote, but can only use it if you reply to a post by each player still alive that day” or “Player Y, you can use ‘detect lies’ on one sentence by a single player each day, but must use the word ‘special’ in at least five message titles that day, please NB me the post numbers by twilight to ensure I know them, you may not say or hint at either your power or your condition for using it or you will lose the ability” or “Player Z, you gain three points every time you vote for someone, to be used towards your point buy role powers, to a maximum of 9 a day, you may not discuss this ability with other players”

Those are examples that are basically ‘posting goals’ but giving a townie a goal like ‘you gain a zeal point for every townie you lynch, which you may spend to make yourself bulletproof or track someone’ or ‘get everyone to roleclaim – doesn’t have to be true, just a claim – and you gain the ability to doc people’ or for scummers ‘Get a roled townie lynched by day 2 and gain a one shot NK’ or ‘get every player to use the word ‘miller’ at some point during the game and you can make one player of your choosing a miller without them knowing about it’


Things to remember during Registration and role distribution
Make a quick list of all new players, and once their role is generated make sure to go through their role message step by step and include otherwise obvious stuff like their victory condition, paste the text of their role straight of the mafiascum wiki if necessary, and include a ‘NB me with any questions’ comment.

Distribute all roles randomly, if you have a role that is simply too complex for a new player, you’re probably better off scratching it, but if it’s core to the game, don’t include new players in random generation for that role.

Don’t mass NB role messages, even to DFs, people can see who else received the message (this has happened) and DFs should not know for sure that they can trust each other.


Game Balance
Trial and error has pretty much identified two basic setups that tend to give about equal odds of town and scum winning
7 players – 2 scum
12 players – 3 scum

That 7 figure works well for new players, how balanced it is for experienced players is hard to gauge, both setups have around half the players as vanilla. Trying to actually expand this for additional players or additional roles in a perfectly balanced fashion is more or less futile.

As a loose rule, in a two faction game of 12+ players, the scum should have 3 goons and the town should have 3 strong roles and 6 vanilla. A scummer is worth about 3 vanilla townies, a roled scummer is worth at least 4. One plain scummer is worth a little less than a cop and a doc combined, by and large.

As a very loose rule, think of a vanilla as being worth 3 points and a scummer as being worth -11 and a roled DF as 13-15, a one shot ability townie as 4, a limited use (3 times and done or every other night) as 5, and a power role (cop, doc, vig, BP) as 6 with any powered up hybrids 7+, an extra one shot NK for the scummers is probably at least -4 itself, as it will remove one townie most times worth 3-6 points. Double the cost at least for any one-shot given to the DFs.

Game of 12, 3 power roles, 6 vanilla, 3 goons
3x6 =18 for roles
6x3 = 18 for vanilla
3x-11=-33 for goons or 2x-11+ -14 scum RBer
Gives you +3 or 0, depending on whether you used a RBer or not.

Don’t treat masons as anything but vanilla, or at most 4 pointers, unless they are day masons or one is an investigator, millers are probably worth only 1 or 2 points instead of a vanilla 3. Any result in the +/- 5 region is reasonably balanced. Applying this backwards to several of the games, it appears to give a strong indicator as to who won and what the general consensus about the game’s balance was, but do not treat the formula as anything but a loose guide.

Actions
The more roles in a game, the more likely actions will conflict, and it’s hard to anticipate them all, for instance, if two NKs target the same person, who hits first? This can be very important if that person is being watched or is a bomb. Is good to map out the obvious iterations but have a method prepared to deal with conflicts you didn’t anticipate, like rock paper scissors or a coin flip or asking a player, any player, to post a message of some random text, even pasted, and take first letter of the names of the players and see which letter pops up first in that text and have them go first, etc… in general however, order of actions can be resolved using this chart:

Find an action such that its effect cannot possibly be modified by any other action.
Resolve it.
Repeat from step 1 until all actions are resolved.

Paradox and Ambiguity
Sometimes the actions that might affect each other form a loop, so that there's no action to pick in step 1. In other cases, the order of two actions matters but it isn't clear that one affects the other. When that happens, pick an action to resolve in this order:
Copy
Hide
Bus
Block
Redirect
Protect
Miscellaneous
Kill
Recruit
Inspect


Checklist – stolen from the 2010 Mod Guide

Is there any way, no matter how unlikely, that this game can be "broken" (made so that one faction is highly unlikely to win even with optimal play)?

Is there any way, no matter how unlikely, that this will go to a Kingmaker scenario (made so that one player is guaranteed to lose but chooses the winner)?

Is it possible for a "tie" to occur (i.e. two players from two different Mafia groups alive at endgame)? If you do not want a joint win, then who has priority and wins the game?

Is there an alignment Cop? with a Doctor? without a Mafia Roleblocker?

Is there a Cult? with normal recruitment mechanics? (This is a good way to get people to hate you and your entire family)

Is there a Jester or Survivor? (Again, this may cause a legacy of hatred)

If the game starts with at least 9 players, can the Town lose without mislynching three times?

Are there a high number of "confirmable" roles? (i.e. a one-shot Vig can be confirmed by shooting; Masons can confirm each other; etc.)

Are there "mod notes" or other facets of the setup that are completely unknown to every player?

Are there any unclarified role interactions where the results could become fuzzy? (Bus Drivers, mutual Roleblockers, and multiple kill flavors are the usual suspects)

Are there any abilities that can be abused? (i.e. Inventors that can ask for anything they like; Town falseclaim abilities)

Are more than half of the players power roles?

Are any of your players given debilitating post restrictions?

If you were playing in a similar game and received any of the roles from this setup, would you be upset with that game's moderator?

If the answer to any of these questions is "yes", your setup needs a second look - at least.