This includes some information that came up in comments on the other post, in expanded form.
1) Question humanity's place at the center of the fantasy world. I think there are a lot of unquestioned assumptions about writing from humanity's point of view. The author simply assumes it has to happen. Whether they're using elves to preach about the evils of humanity or extolling humanity as clever and varied compared to elves, the point is humans, humans, humans. Elves are there to add exotic flavor, either positive or negative.
It doesn't need to happen, you know.
I've heard that humans must be the center of the fantasy world, because otherwise humans can't relate. However, there are books- successful and popular books, in fact- taking place entirely among other races, meaning that fantasy readers will not automatically flee in panic at not seeing red blood and round eyes everywhere. Steven Brust's Khaavren Romances are in a world with human characters, but the main characters are all Draegaran, and humans are represented as dangerous outsiders. The first book of R. A. Salvatore's Drizzt Do'Urden series happens among the drow or dark elves. Humans are thin on the ground in the first part of Tolkien's Silmarillion. There are certainly people who have problems with the books, but they rarely have anything to do with them taking place among non-humans.
Knock humanity out of its automatic, unquestioned place at the center of the fantasy world, and many possibilities open up. You can explore life among the elves without worrying that you must lead back to some point about humans. You can let another race dominate the world without worrying about them having "too many advantages." Few people seem to worry about humans in fantasy stories having advantages over animals, after all; it's just accepted. In a world where elves rule and consider themselves of absolute importance, why would humans have to have an equal place?
2) Non-humans need not share humanity's moral code, take one. It's amazing how often even species very different in lifespan, dwelling place, natural magic, and body shape consider the same things bad that twenty-first-century Western humans do. Murder is always a crime. Incest is always a crime. There are not different attitudes even towards theft. There are often very similar trial procedures, as well. (See my rant on justice and the legal system for why this doesn't work even among humans). The only exceptions to this are races like orcs, who often encourage everything "bad" as mindlessly as the elves encourage everything "good."
Why do non-humans need to share similar morals? Why would they share the same basic assumptions when emotional, mental, physical, and historical differences are present? The goal of not freaking out readers should be subordinate to writing a good story, if it's present at all.
One of my races, the land Elwens, have essentially codified murder. Murder is punished with death, but defined only as an unprovoked attack on another Elwen who does not stand a fair chance of fighting back. Killing for an insult, death in a duel, and especially vengeance on someone who has already murdered a family member or friend of another Elwen are accounted just. It's a necessary mechanism for a race in a highly violent, highly magical world whose emotions are about thirty times human strength.
Such outlets for specific races would make a lot more sense than confining all non-human races to a Western moral code.
3) Non-humans need not share humanity's moral code, take two. The things that humans consider good need not have any place in a society with different mindsets. Probably the most prominent example I can think of is children. Many fantasy books portray elves who are jealous of humanity's fertility, and spend their immortal lives pining for more children.
Why would a race that supposedly lives in utter harmony with the environment and is used to its own long life pine to have unlimited children? They would be aware of what would happen, supposedly far more than humans would, without strict population control. Yet they sigh and whine, because the authors have inflicted a value for large families on them that doesn't match with their experience as portrayed by that same author.
Something is wrong here.
Other human things that many fantasy races value which often don't make sense:
permanent marriage (not practical for immortal or even long-lived races)
permanent homes (unnecessary for people who have a reason to wander)
unchanging traditions (surely long-lived races would have noticed that the world changes)
the same standards of beauty (especially prominent in mixed-race romances, where the male elf somehow adapts human standards of beauty without blinking)
4) Make sure that races are internally consistent in themselves, not only as they relate to humans. Humans visit elven forests all the time in fantasy books, and most of the time note that the elves spend a lot of time singing and pining for the past and wandering through the forest. They go away with moral lessons, usually either "Elves are better!" or "The world will be so sad when the elves leave!"
Now ask yourself if the elves do that even when humans aren't around. Ask yourself if you could write an elven character living in a society like that.
Not so easy, is it?
Non-human life shouldn't depend on the human presence. It might be easy to say that dwarves never do anything but fight and mine, but could a culture that does only that survive? Humans might assume so, but that's because they often see only a fraction, a slice, a sliver, that the author chooses to present to them. The author's mistake is in making that sliver stand for the whole of the race's world.
If the elven forest is like that, perhaps the humans have come on a holiday. Perhaps the next day, when they have rested, the elves will be back to their important work of finding a cure for Dutch elm disease and hunting down dangerous beasts in their forest.
5) Consider some variation of the mixed-race romance. Usually, this is a doomed, tragic love, either because the races are incredibly different in some way (elves and humans are the classic example), or because the mother, of whatever race, was raped. There seems to be no other way that the races can approach each other. Love is unknown. Leaving their own cultures is unknown, despite the straying that must have happened in the first place for them to meet each other. Hell, simple lust is unknown.
This doesn't really make sense, if you think about it. Intense, simplistic hate, as I discussed in the last post, might be easier to write about, but it is not realistic. Nor should the mixed-race hero's parents be the only two in the world to have ever, ever felt that way. Nor should the parents of all half-elves be exactly that way. It's far too easy.
Consider what happens when a human and an elf meet. If they would always hate each other, why are there any half-elves at all? If all romances to produce half-elves are angsty, why? Are angsty elves and humans the only ones to have sex without considering the consequences?
6) If you have a mixed-race hero, represent both worlds vividly. I have a disgust for books where the author shows a hero of two races- human and elf, human and orc, elf and fairy, or whatever- and makes it absurdly easy to see which race the hero "should" choose. Maybe the elven world is perfect. Maybe the human world is really, really great, because they "really live." Maybe- I hate this most of all- the hero has a love interest of either race, and should obviously choose the world that the better person comes from.
For fuck's sake.
If the two races have antagonistic relationships, and the mixed-race hero is raised entirely in one world, then it's likely that he won't even consider choosing the other race. If he's strong enough, he may choose to balance between them. If he's rebellious, he might choose the one that would spite his parents the most. Or maybe this is one of those worlds where the half-elven community is entirely separate, and the character chooses to be half-elf, not human or elven. All of those would be better than the author proclaiming, "Here! This is right! This is the world to choose!"
Maybe more tomorrow. I can think of some more about half-elven heroes especially...