To get your mail opened, give the reader a good reason to want to open your mailing piece. Either specially print your envelopes or print special wording on your labels. About the best example of catching my attention with an envelope was a piece I received from a direct mail magazine. The envelope went something like this (the wording was three lines of bold print across the envelope and about an inch above my mailing label) ...
As I was leaving the office tonight I passed by our subscription manager's open door. Your name was flashing boldly on his computer screen, and his finger was poised directly above the CANCEL SUB key. Panicking, I raced in and ...
The envelope stopped there. I ripped open the mailer, knowing full well this same pitch was going to a thousand other past-due subscribers, but I was hooked. I wanted to know how they ended the story (he saved me temporarily from being cancelled, but he can only do so much, so I better send my money in fast!). You can adapt this grabber to fit the quality and tone of your business. Remember that a mailing piece does not have to only state facts and figures -- you want to be noticed too.