I wrote previously about religious institutions and how they can feature in your game. This post on religion in gaming is all about taboos. Many religions impose prohibitions on people, from the seemingly-trivial to the serious matters of life and death. To the eyes of a typical Western observer some taboos seems strange and petty, perhaps archaic colour of no practical use. As long as we remember that those same Western eyes are observing across the gulfs of time, space, culture and language, we can start to explore the role of the taboo and find ways to apply it to games.
Taboos are sometimes symbolic code for something quite practical. Looking at Dreamtime stories as an example, some prohibitions relate to poisonous plants or animals that the hearer will remember and use to survive. Disguised survival lessons also work in the positive, weaving the location of a billabong into the events, using geographical markers found in the local area. In your game, you could use this to show plants or locations that the locals avoid, and then open an adventure to discover why they avoid it, and perhaps have the players face that danger. They could unwittingly consume a poisonous substance, or bravely face the demon. Be sure to have the locals show fear, perhaps superstition, about the taboo. Mothers will snap at their children for mentioning it.
Sometimes taboos exist to manage procreation. Aborigines in central Australia have a complex system of totems showing which people can have children together without the risk of birth defects. Use this in your game to start a story of forbidden love, or a story of devotion to a child born from forbidden love and now living with some kind of genetic defect. It could be as fantastical as a quest to find a magic cure, or as dark as a secret that should not be exposed (Perhaps the prince has a forbidden lover, and the child is proof of breaking the taboo, costing him the throne...)
Dietary taboos are prevalent in some religions. Don't eat pork of shellfish. Don't drink alcohol. These dietary restrictions can be signs of devotion or cultural markers. As devotion, they are personally important to characters, but can cause problems. Supposing a non-drinker wants to do business in a culture that prizes bargains over drinks. Devotion and cultural markers can turn bad and become a source of condescension or disgust. After all, if that food isn't sanctioned by the gods for human consumption, then we can question the humanity of anyone who does eat it.
The last one for today is misogyny or misandry. In our own history, taboos about women have been used to enforce patriarchal structures of power in society. Are men and women treated differently by the religion? Use this to establish etiquette in the game, and then conflict by breaking those traditions.
In general, religious taboos can be a source of story in your game in a number of ways. Think about what the taboo is and how it marks out the people who hold it to be forbidden. Consider what happens when they are in contact with the "unclean" neighbouring peoples. Consider what happens when people break taboos. Taboos might be arbitrary, or practical, or just something that a petty deity despises. The addition of a taboo to your game setting immediately acts as a creative constraint that can generate plenty of story for your characters.