And back to the questionnaire format again. This time, some things that I tend to consider when setting up a religion.

1) What are the core principles of your religion?

These are essential. I’ve read a lot of fantasy religions that have detailed descriptions of temples, high holy days, decorations that people wear at certain times of the year, the raiment of the priests, rituals that people perform before plowing their fields, and so on, but have no heart.
What does this religion stand for? If a worshipper who is typical of a particular region—or world, if the religion is global—were asked to boil down the principles of his faith to the most important ones, what would he choose? Probably not the holy days and the decorations, unless the faith has become one of those distant ones more honored in the breach than the observance.
When an author doesn’t consider this, fantasy religions have a tendency to default to one of the two models that a lot of authors base their faiths on anyway, Christian or Wiccan. Either the religion is based on forgiveness, love your neighbor, and so on, or on love of nature and worship of the earth and following of a distinctly agricultural calendar. Never mind that in some cases this doesn’t make all that much sense. There’s no reason to think that a polytheistic religion, or for that matter a monotheistic one with a goddess at the center instead of a god, would follow the same code of brotherly love as Christianity. And what about people who live in some other setting than the typical mix of forests and fields and towns that makes up a lot of pseudo-medieval fantasy worlds? A desert people are highly unlikely to “love the earth” and “conserve the trees” if they live in a place where the earth is so hostile to them and trees are rare. They might have an adapted religion, if they were originally Wiccan-like and then moved into the desert for some reason, but it should not be exactly the same.
Come up with a core of principles that make sense in your world. How do they survive? What gods might they think are responsible for survival? What entirely practical tasks could get hardened into religious rituals because they were important to the continued thriving of the people? (For example, I’ve read a few post-apocalyptic novels that hardened things like washing hands into religious rituals, because without them diseases would kill people). What wars, monarchs, invasions, rival religions—see point 4—have influenced the choosing of sacred sites, the honoring of certain days, the decision to worship a certain god and not another one? For that matter, is this really a centralized religion whose principles are consistent from one village to another, or is the decision to call it one faith more academic, with people in farflung places worshipping whoever the hell they want? There’s no need for a centralized church, either, though some plot ideas can become easier if you have one. In places where people are separated from each other by immense cultural or geographic or linguistic barriers, it would make more sense not to have one.

2) What are the relationships of the gods with each other?

One reason, I’m convinced, why so many fantasy gods sound bland and soulless is because the author conceives them in isolation, and gives them stock personalities only rivaled in blandness by the Basic Healer Personality. Of course Misheat the Fertility Goddess is calm and loving and giving; what else would she be like? And what “relationship” does she have with the moon goddess, who of course is virginal and chaste? What does it matter? They’re both just there, often to be plot conveniences.
Not so. If you have a family of gods modeled on the polytheistic pantheons of the past, go and study the mythology and see how they interacted. There are dozens of stories in Greek mythology that can’t be broken down simply into “These gods were like this because of what they represented.” Why was Apollo the god of poetry, medicine, and prophecy as well as the sun? The reasons for associating those things are complex, and in the case of prophecy, it’s because of a different legend than him as god of the sun, that he killed the Python and took its oracle away from it. He also overindulged one of his sons so much that Zeus had to kill him to keep him from burning up the earth, lost a young man he loved because the jealous west wind blew his discus the wrong way, and pursued the maiden Daphne, who turned into a tree to escape him. There’s a god with some personality. Yes, those legends generally explain the existence of something, such as the Daphne legend “explaining” the laurel tree, but they accreted ideas and personality traits that don’t strictly need to be there so that a listener may understand the explanation. Do this if you want to keep your fantasy gods from sounding like bad copies of D&D pantheons.
Of course, you might have a monotheistic “pantheon,” or a world in which you’re interested in keeping the gods from direct interaction with each other. Why wouldn’t the peasants still make up stories about them, the poets compose songs in honor of them, and the academics still argue about what is true or what is false? There are tales of Christians and Jews fighting worshippers of other gods, for example, and though the Roman relationship with their gods has been described as dispassionate, there are still immense epics that include them. Whatever the metaphysical truth, holy legends tend to accumulate stories around them. Go forth and build them.

3) How do the gods interact with mortals?

The answer in too many fantasy novels is, unfortunately, “in such a manner as to put the reader to sleep.”
The usual idea here is that the gods are so powerful they could just wave their hands and make everything good and nice by deus ex machina right away, so the author must keep them in the background for the good of the story. This relies on a number of faulty assumptions, however:
a) First, that the gods can simply act without restrictions other than their own wills. What about other gods? What about metaphysical laws that might prevent some tampering, but encourage other kinds? What about the gods’ own magic being subject to or countered by other kinds of magic?
b) Second, that all gods are omnipotent. That’s another of those basic, unquestioned assumptions that migrates in from Christianity. If a god is not all-powerful, then his or her tampering in the story might be a matter of life and death for the god, though still not much fun for the mortals involved. Or he or she might be omnipotent in his or her own sphere, but what happens when they want to do something involving the sea and they’re not the deity of the sea?
c) Third, that the ways the gods do appear in the story are somehow not tampering. I personally feel that the goddess appearing to give a vision to the heroine, or showing up at the end after being freed from a prison to face the evil god, is far more boring and stupid than a meddling goddess sticking her nose into everything. Why is it not cheating for a goddess to give the heroine the vision that is the key to the entire plot, but it would be cheating for the goddess to fly the heroine to her dying brother’s side? Authors proclaim that they must keep the gods distant, then turn around and add them anyway. Do follow your own rules. Either the gods are distant and cannot be reached, at all, as the author usually proclaims, or they are present and infused in everything. If they’re distant, then nobody’s rituals or prayers or appeals should bring visible help, and that includes the “Chosen” heroine’s.
Of course, you don’t have to follow either of those two extremes. The gods can poke in, out, and about, plan and play against each other, be very random (especially if they’re trickster gods), be too busy to bother with humans, be Deistic gods that created the universe and walked away, or anything in between. I would actually like to see some gods who’ve just retreated to their cloudy heavens and refuse to notice anything going on on the silly earth. The problem is that the fantasy author says that’s so, then brings in the “Chosen” heroine without explaining why this aloof goddess makes an exception for her.

4) How does your religion treat apostasy, heresy, members of other religions, and atheists/agnostics?

Unless the religion is truly global, it should have problems. And even then, the priests are probably killing heretics behind the scenes.
If you’re unsure about what kind of troubles religious conflicts with other religions can start, go read some history. It can even be just Christian history. Wars of religious faith are probably the bloodiest and the most vicious, and in a world with humans or creatures who have enough human psychology to have developed religion, they would most likely surface.
Here, the tendency not to think things through deeply enough rears its ugly head again. Too often, when fantasy authors handle religious conflicts, they do it by designating one religion—most often the goddess-worshipping, nature-loving, woman-dominated one—as “good” and the other—most often god-worshipping, technology-loving, male-dominated one—as “bad.” It makes for cardboard characters, stock villains, and a world in which Darkness and Light face each other and must, of course, battle to the death. The Darkness is calling demons, you see.
It makes me scream in frustration. It makes no sense. If someone is going to worship “evil,” they better have a damn compelling reason, and they need to be stupid enough to ignore the “evil” god’s usual record of killing his servants. It’s really, really difficult to get those two traits to exist together believably. Also, too often the “good” religion’s standards get applied to the other. Creating technology is seen as evil because the goddess-worshipping people don’t do it. Likewise with summoning demons, calling ghosts, using blood in sacrifices, or whatever it is.
Besides, what would those smug people in white robes do if they had division in their own religions? Probably only rebel groups are more prone to have factions. Christianity, when it started getting powerful, had to face and suppress heresy after heresy. Divisions between various branches of all the most powerful world religions are present. Even a relatively new religion, like Wicca, can have dozens or hundreds of different opinions about what should be done with it. How do your people react to heresy? How do they try to punish it or convert the opposing factions? What caused the division in the first place? Why can’t it be healed? What is going to happen if it isn’t healed?
Finally, where are the people who don’t accept the gods? Atheist characters are practically nonexistent in fantasy, even in ones where the authors do manage to keep the gods credibly distant and therefore no one has any idea whether or not they exist. So are agnostics, people who don’t know about the gods one way or the other, but are not prepared to make a proclamation of knowledge. (Agnostic literally means “without knowledge.”) In many fantasy worlds, there are conditions that should see them sprouting like mushrooms after rain, yet everyone simply believes in the gods. Do they keep quiet for fear of being punished? Do they just not care? Do they really not exist, and if not, why not? This is the kind of issue, like heresy, that authors with powerful religions need to consider with care. And just the existence of a religion is no guarantee that someone will believe in it. Go read Pratchett’s Small Gods, in which Om is reduced to a manifesting as a tortoise because, despite his great and powerful church, almost no one believes in him.
Religion is a big conflict-provider in fantasy, handled right. The problem is that fantasy authors present whitewashed versions of it (just as they tend to do with battles of the sexes, romances, the conflict between good and evil, and everything else).