Founder and CEO of Auctions Systems Auctioneers and Appraisers, Deborah Weidenhamer's biggest piece of auction advice is to do your homework. Make sure to check out the item during the preview period when you can inspect it thoroughly, particularly since everything at auction is sold as-is, where-is.
You should also do a fair amount of market research to determine an item's true value and then check in with your budget to determine the dollar amount that you're willing to bid up to. That way when you're in the heat of a bidding war, you'll be well-informed and can make good bidding choices. Otherwise, you could run into the dreaded Winner's Curse.
According to Weidenhamer, "The theory of the winner's curse, which I don't actually believe is true, is that the person who knew the least about the value of the item is the one who pays too much." This is an unlikely scenario given that most auction items sell for their market value. But for the bid-happy, the bottom line is research, research, research.
On the other side of the coin, if you're in the market to unload your own treasures you may want to scour your own attic for any unused items and keepsakes. They may just fetch a pretty penny at auction.