For any campaign setting, you need to define the races and their interactions. The easiest way to do this is to start by confirming or eliminating each of the basic races.
Humans are in. They are generic and make a fantastic point of reference. They may not be the most powerful race, considering the longevity of other races, but we'll see.
Dwarves are also in. It's hard to rule them out, since they are a staple of fantasy. They may not end up quite like the usual stereotype.
Halflings are in, and will be made into a race that has more influence than they do in most current campaign settings. I like the idea of them, but they always get shortchanged in campaign settings.
Elves are in. I'm not sure yet exactly how I'll paint them in terms of interaction with other races, but they are definitely in.
Gnomes are probably out, at least as a major race. There might be a few tinker gnomes in the world, but they won't be common. I don't want the world to have too many gadgets, and I like my gnomes to tinker.
Half-elves might be in, though they may be tweaked a bit. They've always fit in too cleanly as their own race for my tastes. They will probably be second-class citizens in my world, showing the disdain of both humans and elves for these half-breeds. There may also be some tribes of them, living by themselves to avoid the constant judgement of full-breeds.
Half-orcs are out. I have never liked the idea of them. And the orcs in my world will be a bit more like the Reavers of Firefly--they don't leave survivors.
Planetouched are out. There may be extraplanar beings, but they will not be a playable race, nor will they be all that common in the world at large.
In fact, I'm going to go ahead and call it good with the list I have so far. Humans, dwarves, halflings, and elves will be plenty of civilized races for the world. Now, subraces are an interesting way to create further divisions AND create reasons for allowing interracial parties.
Humans might have a subrace or two, but they'll be common anywhere, so it won't matter too much. And they won't divide by subrace, but by political group.
Dwarves will be available in both hill and mountain models, each having their own features. The hill dwarves will be friendlier to other races, while the mountain dwarves will do some trading, but keep their amazing cities hidden from prying eyes. I see the hill dwarves as having a simpler life, and being more open. The mountain dwarves will be industrious, but they'll keep mostly to themselves.
Halflings will remain the jovial sorts who have several breakfasts a day, just as they have been since Tolkien created them. The difference will be in a certain diplomatic cunning. They'll be prolific traders, and have treaties of protection with virtually everyone else, keeping their non-warlike kingdom safe..
Elves will come in three flavors. High elves will have a magnificent kingdom, but will allow only others of their kind full citizenship. They will grudgingly engage in trade, but try to have as little contact with "lesser races" as possible. Wood elves will be elusive and somewhat secretive, but not unfriendly. They will be self-sufficient and engage in very little trade, but will be friendly in interactions with other races. Their cities will be hidden in the forests, perhaps magically. The third breed will be aquatic. They will be a mythical sort, and not allowed to players. They will sometimes aid sailors who find themselves at sea without a ship, but they will have very little interaction with the land races.
Most half-elves will be the progeny of wood elves and humans who spend substantial time in the forest, though some high elves will indulge themselves with the lesser breeds, bringing great shame if they are found out. Wood elf half-breeds can never find the cities of their elven heritage if they ever leave. Humans will also be cruel to the half-elves, generally mocking them for their perceived fragility, marked elven features, and alleged effeminate nature. Female half-elves are more accepted than males, though they are treated only as sex objects or serving girls, with little respect afforded them. Because of their problems in any civilization, half-elves sometimes band together and build their own villages, generally in or near halfling land, where they are accepted.
You'll note that I have shied from the notion of evil races. There are going to be the monstrous races, which will be savage and sometimes evil, but there will be no calculating evil races like the Drow. There may, however, be evil kingdoms. It has never seemed right to have an evil race. I may change my mind, but I prefer to think of evil kingdoms as being a regular race that has allowed a cruel regime to take power or has harnessed the power of some evil magic. But we'll see.