I swear I'm not trying to plug my own site, but I just wrote an article on this very thing earlier today. It's part on an ongoing series I've been trying to find time to write. It's really weird that I came across this in the same day. Here's the portion of the article that deals directly with your question.
Races
How many races will you have? Each race increases your work exponentially, because each race represents at least one separate culture (and probably has multiple subcultures,) which requires details for a multitude of factors.
* Languages: How do races speak within their race and with other races?
* Government: How is order maintained? Who makes the rules? Who enforces them?
* Politics: who are the power players, and what are their agendas? Are they violent, passive, or something in between?
* Arts and entertainment: what do these beings do for fun? Do they have music, sculpture, painting, games of chance, games of skill, written language, or formal education?
* Technology: How do they communicate or travel over distances? How sophisticated are their buildings, fortifications, weapons, armor, medicine, astronomy, chemistry, and other sciences?
* Economics: How are goods and services exchanged? Where is the supply? Where is the demand? What goods and services are produced? Who wants these products?
* Religions: What do these beings believe? What impact does religion have on the rest of their society? How many different religions are followed by the race, and do they tolerate each other?
* Environment: How does weather and topography affect the race? What do they eat?
* Other: What about holidays, calendars, time keeping, taboos, superstitions, and prejudices?
Please feel free to
check out the rest if you feel so inclined.