"If you want to increase the odds that someone keeps your business card when you give it to them, add something valuable to the back of the card that makes it worth keeping.
For example, you could have a industry specific reference guide printed on the back. Or a calendar. Or a football team's schedule. Or a list of important phone numbers. Or first aid information.
The goal is to have something your target market finds useful enough to carry around in their wallet - with your business card printed on the front."