A good business card should be readable. Avoid clutter and make sure that one can clearly see where a given piece of information starts and ends. It is advisable to use fonts such Helvetica or Myriad Pro and a font size of 12pt. Using a size smaller than 12pt is highly discouraged for it may be challenging for people with visual problems to read it and, while it might make it easier to add more information, it also make it easier for you to clutter your card up.