Recruit pitch-perfect voices.
Invite friends who can sing on key. Members of a church choir or other singing group would be perfect.
Invite spirited friends.
If friends can't hold a tune, tell them they can help decorate your tree, so they won't feel they have to sing. Chances are they'll join in the caroling anyway.
Ask guests to bring their favorite scarves, hats and mittens to get the right look.
Stock up songbooks.
Buy books of Christmas carols for your guests. Make sure everyone will have a copy since many people do not know every verse to every carol.
Make candle holders by poking holes into paper plates if you plan to carol outside. Slide the candles through the paper plate. These candles will provide light so people can read the lyrics.
Reward your revelers.
Plan to have a variety of finger foods, cold and warm, and a variety of drinks, including hot chocolate to warm up the carolers after their singing adventures in the cold.