Werewolf is a great filler game with a larger group, and a superb way to break the ice at a geeky party or convention. But when the opporunity arises to play, there's always that frantic moment of scribbling roles onto scraps of paper to set the game up. Dicecards contain a full set of roles for up to 24 players.
The rules for how to play can be found here, or on many other sites around the internet. The game is a retheme by Andrew Plotkin of the game Mafia, by Dimitry Davidoff. If you are looking for more information, try searching for both Mafia and Werewolf.
24 dicecards have a werewolf role on them. If you intend to use them, it is worth sorting out the right number of cards beforehand, and shuffling just the roles you need. The number of werewolves you need depends on the size of your group, for 6-11 players, I'd suggest two werewolves, for 12-16, have three, for 17 or more, have four. Make up the rest of the numbers with villagers. If you chose to have one or more special roles (see below) use them in place of a regular villager.
Special roles can liven up the game a little, and add an extra strategic dimension. There are literally hundreds of roles that have been proposed, but dicecards contains the most common or most fun (in my experience). If you want a different special role, then just substitute it for one of those in the pack (i.e. say "if you get the cupid card, we are not using cupid, that card means you are the 'witch'").
During the first night, after the werewolves have gone back to sleep, the moderator asks cupid to wake up and point to two people. These people will be lovers for the duration of the game (the gender of players is irrelevant). The moderator then walks around the circle and taps the two lovers gently on the back. These two then open their eyes and identify each other. The goal of these players changes: their only goal is to make sure the other survives. If one is a villager and the other a werewolf, then this can only happen if they work together to eliminate everyone else in the game. Lovers still act as if they were their starting role (i.e. werewolves still wake at night with the others), but they will never vote to kill their lover. If one lover dies at any time, the other lover immediately commits suicide, and reveals their card. After the first night, cupid acts as a regular villager.
The hunter is a regular villager, but handles death slightly differently. When a hunter is killed (either by werewolves in the night, or as a mistaken lynching), they can shoot any other player in the game. They point at their intended victim (they still may not say anything after being killed). That player is then also killed, and reveals their role. A hunter may chose not to use this ability.
The seer is a regular villager, but gets a special action each night. After the werewolves have gone back to sleep, the moderator asks the seer to open their eyes and point to any other player in the circle. The moderator then puts their thumb up to indicate that person is a villager, or down to indicate they are a werewolf. The seer may freely share this knowledge during the day, but doing so makes it much more likely the werewolves will kill them the next night, so care must be taken.
The child is a regular villager, but can open their eyes during the night to observe the deliberation of the werewolves. This power cannot be used on the first night, when the werewolves are first making contact. If the werewolves spot the child looking, they will most likely choose to devour them, so the child must act discretely. Note that this role usually biases the game very strongly in favour of the villagers, so you may want to add one more werewolf than usual if you are playing with this role.