Some things that look fun on paper to the host can turn out to be terrible in actual play. On the other hand you'll never hear anybody complain if you use 50%+ Vanilla Roles in your setup. It's easier to understand it once you've hosted and played more games.
A few tips:
* The minimum amount of phases it takes for either faction to lose should be equal or no more than +1 in town's favor [3v3 or 3v4 in town's favor is the standard in dGames for setups with 3 mafiosi].
* Don't use Closed Masons, Watcher, Vigilante, Serial Killer and Cop. These roles tend to break setups.
* Avoid Janky roles like Cult/other indies, Traitor, Doublevoter or Bulletproof. You can't know how to balance them at this point.
I have a thread that lists a whole bunch of roles and how easy it is to balance them but I'd have to dig it out first.