Well, first there's the thing with the race's original habitat:
1 - Dwarves live in and under mountains, clashing with the foul things that threaten them from below. They are forged into a martial race, with extreme sense of devotion to the greater good of dwarvendom. Their opposite number are duergar.
2 - Elves live in forests, protecting the plants and animals from devastation from the careless/evil/shortsighted races that would plunder them. They are a wise race that sees themselves are the caretakers of the world. Their opposite number are drow.
3 - Halflings live wherever they can, then move on. They have to deal with different situations on a daily basis, so learn to make the best out of even the worst-case scenario. Their opposite number are goblins.
4 - Humans live wherever they can, like halfings, but tend to settle once they've tamed the area. They learn to out-think almost any difficulty. Their opposite number are orcs.
5 - Gnomes live in swamps and the hills they surround. They are threatened daily by not only savage creatures, but also by the symbolic corruption of the swamps. They learn to misdirect their foes and cloak themselves with magic. Their opposite number are kobolds.
6 - Half-Orcs live wherever they can, but they have to fight to make a niche for themselves. They learn to be strong and to have a "give no quarter, take none" attitude. Their opposite number are half-elves.
7 - Half-elves live wherever they can, but learn to use wits and charm to make a niche for themselves. At the most basic level, they can weasel themselves into society. Their opposite number are half-orcs.
That's all IMHO, of course.
