Blades in the Dark has a really interesting "cult practices" table, and there are similar tables/generators on-line that could help. Here's a decent-looking one that just came up from googling:
https://www.reddit.com/r/DnD/comments/89km68/god_complex_random_fantasy_religion_generator/
Some of my own ideas:
- A cult of assassins who worship the god of death, who are forbidden from taking life UNLESS someone else asks them to do it.
- A religion of a fire-god who believes that the color orange is divine and forbid its use on anything except holy symbols.
- Followers of a moon goddess who believe each phase of the moon favors certain activities and attitudes.
- A highly lawful church whose members are forbidden from making promises that are not in writing.
- Worshipers of math and geometry who regard interesting shapes as auspicious.
- A god of both life and death, whose clergy function as both doctors and executioners.
- A culture whose dominant god has declared a particular flowering vine as a sacred plant; in their towns and neighborhoods, that




grows everywhere.
- Bathing. For whatever reason, a particular god demands their followers bathe on a strict schedule (or NOT bathe for extended periods).
- Every 7 years, members of this religion gain a new name. They always introduce themselves by their most recent name, and you can tell how old they are by the length of their full name.
- Communities of this sect are forbidden from exceeding 144 adults in size; a community that grows larger than that must send some of its members elsewhere, or establish a new settlement.
- The church of a prosperity god functions as a bank; churches are gaudy, heavily fortified, and provide micro-loans to members.
- Children and converts are sent to be judged by [ pixies | unicorns | druids | blink dogs | celestials | giant eagles | a gold dragon ] and are not full members of the religion until they are deemed worthy.
- An order that forbids members from owning more than they can carry, so members invest in superior backpack technology and wear a lot of heirloom jewelry.
- Secret graffiti: followers are encouraged to put their god's symbol or mark in all kinds of weird, hidden places, where it will turn up later.