If you’re running a hundred or more auctions a week, you want to draw attention to your auctions. That might mean splurging for some of eBay’s listing enhancements (boldface, gallery, and so on), although these extras typically aren’t worth the extra cost. Better to promote your auctions on your personal website, via message board postings, and in all your emails.
Probably the most important type of promotion, however, is word of mouth based on your good reputation. You want to encourage repeat bidders and drive buyers into your online store (if you have one) for additional sales. That means treating your buyers fairly and with respect, and going the extra mile to ensure their satisfaction. It also means sending previous buyers emails when you have items up for auction that they might be interested in. (Which argues, of course, for keeping comprehensive records of all your eBay auctions.)