Start with just the physical qualities of the card.
You want the card to do the speaking for you when you're not around. When someone has a Rolodex of cards and they're deciding who to call, it's a subjective thing. So you want to make sure your card works the way you want it to.
Tell somebody more about your business than just your name and address. List some services that you provide. If you're a dentist and your practice is made up of kids, get that across.
We also have web addresses and e-mail addresses on business cards. As a result, some business cards are starting to look very crowded.
You need to gear your type size so that a person of any age group can read it.