Whether a live or silent auction, variety is the key. You'll find profits will increase and attendees will have more fun if you offer a variety of values throughout the event so that everyone gets a chance to participate, make a donation, and contribute to your cause and the event's success.
During your live auction, don't put 10 dinners up for bid in a row, intersperse both the type and value of items. Start out with a moderate priced item; if the bidding starts out with expensive items, part of your audience will assume that the entire offerings are out of their price range and leave or ignore the rest of the bidding. If too many lower-priced items start out the evening, the high-rollers lose interest.
Any easy way to enhance the variety of items and values is to sprinkle in fixed donations. Periodically throughout the bidding, include simple pledge requests, such as "$80 to supply Paper for the Month." The donors enjoy knowing directly where their donations will go and it provides a great option for those who are not in the market for any of the other goodies that you have on offer that evening. If you do specify what a donation is used for, be sure and make a note so that these funds will be used for the item stated.
Providing a selection of items and values will keep your bidders excited and attentive - both which will help create a successful event.