Direct-mail marketing campaigns can be an art & science. There are many studies and lots of data suggesting what works and what doesn't. In many cases, these are sent to strategically-targeted groups of strangers, based on mailing lists that are purchased or collected over time. My approach to this is similar to my approach to advertising design...just GET PEOPLE TO READ IT! (And keep it out of their trash can!). This page also features a number of specifically-targeted invitations for personal friends, family, work colleagues, or a company's customer contact list/database.