Mail repeatedly to the best attendee prospects until they say, "Stop! Iíll come." Usually these are past attendees and this year's inquiries.
But you must vary the look or message each time. For example, begin with a conference brochure and cover letter. Then do an e-mail broadcast. Next, a conference brochure without cover letter. Finally, an exhibits-only piece that screams, "Last Chance! Act Now!" Itís a fact: even the third or fourth mailing to prior attendees and inquiries has a better response rate than the first mailing to other lists.