4. Arrange for attendees to bring a homemade potluck item so there will be non-swap snacks, and you're not put out to feed and entertain 20 people. Food people like to bring food to events, trust me. Everyone wants to show off something they took the time to prepare. Adding a potluck feature also opens the event to people who maybe don't have a swap item, but would like to join in the food fun with a group of like-minded friends.
5. Have tags pre-made so you don't spend the whole party explaining to people what to write and how the swap works. We initially cut 3x6" index cards in threes and allowed partiers to fill-in our categories accordingly. Then we created this document, which you're welcome to download and use at your swap.
Our categories include: What (is the item to be swapped), Who (is the swapper), and Offers listed by Name/Item (Who to talk to and what will be offered in exchange). We leave room for 10 offers, hot items can continue receiving offers on the back of the card.
Let your swappers know that writing your name on something does not mean you will get it. Actual swapping takes place via discussing exchanges. The names on your item's card are good places to start when you begin chatting and swapping since the people listed already want your item. (My swap strategy involves scouting out what I'm most interested in taking home, regardless of whether the items' owners wrote their names on my sheet!)
6. Designate a time when the swap will take place within the context of the party. Our parties last for about 2 hours, and the swap usually happens at the start of the 2nd hour. This gives guests time to assess the table and make their top picks before being thrown into the pit of chatty swappers vying for delicious goods.