Business cards, like caption pages, have to fit a lot of information in a small area. But they often try to do too much.
For instance, the card layout below is fairly common among lawyers. I call it the baseball-diamond layout: information is pushed out to the corners, and your eye has to travel around the edge of the whole card to read everything.
The guiding principles with business cards are the same as with letterhead. Remove anything nonessential. Don’t worry about the text being small — there’s not very much of it. Build the layout from the text outward. The white space will take care of itself. If you work from the edges of the card inward, you’re more likely to end up with a baseball diamond.