A series of humorous rants on how not to do it - because I, for one, have seen enough amateur fantasy to write a book on the subject. And one day, I just might.
I think there are two ways to worldbuild. If you're writing a short story, your world should be character-based. You should be thinking about what you need to tell the audience and tell it. If you're writing something like epic fantasy, then your characters should come from the world, not the other way around.
Think about it. Let's say I have a world similar to Earth. Let's say I add...elves to it. (Oh, the cliches... just bear with me here.) Okay, so how are the elves going to interact with the humans? Chances are there will be some differences between the two races OTHER THAN THE POINTY EARS. Let's take another few cliches here, and say that elves are taller, more slender, and better archers. *headdesk* These cliches are killing me here, people.
Anyway, back to the point at hand. Most amateur writers will leave it at that. Well, no. That won't WORK. You can't change one thing about the world and not change everything else. Ripple effect, people. You can't isolate a ripple in a lake. You just CAN'T.
So, what would you do with these overly-cliched characters, then? Well, think about it. If the elves are better archers, they're going to have a huge advantage over the humans when it comes to hunting. They'll shoot down most of the animals before the humans can even string their puny bows. Assuming that both races live close by (to enable interaction, which had BETTER be crucial to the story), this is going to hurt human development badly. They might all have to turn vegetarian. They might become adept with hunting knives instead. They might start slaughtering the elves.
If you decide to take the vegetarian route, then have other things progress from this. Some sort of religion could arise from this that involves treating animals as equal to humans, so hunting is as bad as murder. That could lead to devising some nasty punishments for those who break the law. And before you ask where this idea came from, think about it. Humans will do ANYTHING to convince themselves they have no weaknesses. So if they can't hunt as well as the elves, they'll say it's because animals shouldn't be killed, rather than admitting their own flaws. Also, some prejudice will eventually build up against the elves, and this will probably lead to some pretty nasty things. (Don't try telling ME that vegetarianism doesn't lead to genocide!) If you want some ideas on how nasty, look at Christian/Pagan arguments. Because I'm fairly sure that the humans would see the elves as some sort of dark, evil species for killing their animals. Of course, you could go one further and have the humans worship the animals as sacred, which would prevent the elves from hunting as well - if they laid a finger on an animal, war would break out.
So let's say that you choose to have your humans develop skill with hunting knives instead. I can see a lot of rivalry building up here between the two races. And don't try telling me that the two will co-exist peacefully, with the archer elves shooting birds to eat and the humans hunting only on the ground. It won't happen. Sooner or later, some elves will shoot a groundling, or a human will invent throwing knives. It's wanting more than they need. It's called greed. Humans have it, and if your elves are believable, they'll have it too, even if they try to hide it. And war will erupt.
Finally, let's say you decide to skip both of those stages and have the humans start to slaughter the elves as soon as they realise that they are better hunters. Hm. My first thought on this is that it's rather stupid. Admittedly, they'd get in a good first surprise attack, but after that, they're doomed. If the elves are better with bows, they'll start massacring the humans as well as the animals. They might even start eating the humans (It's not technically cannibalism as the elves are a different race, so stop making spewy motions). If you have any other sentient creatures (if, say, the pigs were able to talk), you might want to think about an alliance, either with the elves, to avoid slaughter, or with the humans, to fight back and hopefully put an end to their race getting eaten. If you have your cliched elves have a cliched attitude, they might refuse the help of these creatures and continue to slaughter them as food. They might use them to help destroy the humans and then destroy the creatures afterwards. If the creatures side with the humans, it won't mean much. Sure, you might have a moral victory, but at the end of the day the bloodshed will continue. If the elves are able to hunt the creatures, then the creatures won't be that great an ally for the humans. They'll just be a liability on the battlefield. And even if the humans are great with swords, if your elves are the typical masterminds that they're portrayed as, they'll shoot the humans down before they and their swords can even get CLOSE.
OVERALL SCORE: Elves 3, Humans 0.
XD Joking. Seriously though, that's why you have to think about these things. If anyone can justify having the original situation of a cliched human/elven world where the humans survive (regardless of the elves' survival), tell it to me. If you can find a loophole to human inferiority, I will give you a prize. The moral of the story being, DON'T MAKE THOSE ELVES SO GODDAMN SUPERIOR.