Probably old news to most APF members, but you should sign up for a sniping service.
I recommend gavelsnipe.com, b/c it's free and allows you to snipe at three auction sites: eBay, HA,and MPExchange.
On eBay, I recommend you first make a reasonable bid on eBay to discourage the seller from canceling the auction early due to lack of interest. Then make your "real" bid through gavelsnipe.
For HA, keep in mind that your snipe bid will be placed on Sunday night before the final "live" auction begins so your bid can be topped