If you're going for a fantasy realm, don't fall into the same tropes regarding races. We've all seen the pretty, elegant, arrogant elves and boisterous dwarves. Make new archetypes, or spin existing ones at a different angle - for example, make dwarves deadly serious, tradition-bound, and scary tough to kill.
Above all else, make the world internally consistent.
Above all else, make the world internally consistent.