Instructions
Ask everyone to contribute some money each night. This doesn't have to be very much--five dollars or so per person--but it raises the stakes of the game and makes people more engaged and competitive.
Serve food. Bunco nights generally take awhile, and if you make them an evening-long event--complete with appetizers--people will be happier and more relaxed.
Ask your guests to bring a plate if you don't want to serve food yourself. Combining Bunco with a pot luck can make things more fun.
Serve drinks. Drinks loosen people up and make the game more exciting and emotions run higher. Obviously, there's no need to get completely plastered, but a few drinks each won't hurt anyone.
Take a break halfway through. While Bunco is fun, people will enjoy themselves more if they have a chance to decompress and talk amongst themselves for awhile.