Any tips about balancing a setup?

[FakeGod]

Basic things to consider:

Do a probabilities calculation/test run assuming random lynches every night and aim for 50/50.
Make sure there is no easy way to break the setup. (defend your setup vs an early massclaim at least)
Don't rely on one role to fix your setup. (i.e. relying only on a mafia roleblocker to counter a doc and a cop)
Will flavor be useful or not useful in actual gameplay? Does it matter if only half the players know the flavor? Can they be mislead by the flavor? (A Harry Potter claim in a Harry Potter Flavor mafia might have additional weight to it than you might want, etc)
Priority of the night/day actions need to be set in stone beforehand. (How does roleblockers interact with jailkeepers?)

More things to consider:

Town tends to be discouraged if there are no mafia flips for awhile. I'm sure you can design a 12 vs 1 setup that has a superpower mafia role and technically balanced, but do realize that town will be seeing town flips after town flips for a long time, and they're probably going to hate it.
Post-Restrictions might be funny for couple posts, but will the player enjoy it for the rest of the game?
Unless it's bastard setup, putting in actions that rely on random chances is discouraged. (enabling the players will let them have fun; letting the game be dictated by random chance outside of any players' control ensures that players stop having fun)
Make sure all possible endgames are accounted for in your wincons. If there are 1 Mafia A scum, 1 Mafia B scum, and 1 town VT, who wins?
Never make your wincons ambiguous.
Consider extreme cases.
If you can, design your game so that it favors the scum slightly if town is random lynching. (for example, Assassins in the Palace is a setup that favors town given random lynches; ergo, best town strategy is to quicklynch without discussion; try to avoid that if you want a game that isn't series of quicklynches)

[FakeGod]

If you can, design your game so that it favors the scum slightly if town is random lynching.

Not usually a problem. <.<

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When there's enough VIs in your game, anything becomes possible.

[FakeGod]

The prevailing thought in F11 newbies was that if a Mafia Roleblocker got lynched D1, the scum team deserved to lose.

Well, that's just poor.

I don't think any one lynch should be that much game breaking, especially in a newbie game.