Creepy Party Decorations

You could paint the face like the face of a famous celeb - dead, or use masks of a skull, a witch or a fanged red eyed vampire. Or you could use an all white robe and white long gloves. Ask your guests to come dressed in creepy characters according to their choice.
Sling spooky masks from the walls. You could also fill your party room with elegant china and silver, candle bras, trays filled with fake pearls and jewels, drapes of fancy fabric from the fabric store. Use candles and soft lights, or shaded lamps in a way that creates longer than usual shadows. The party will indeed be creepy with the use of colored lightings, potted plants covered with dark colored robes. You can also use candles for a creepier ambience. Ask your guests to talk in a very soft or whispering voice for the first ten minutes or so. You could also use a creepy music as a final touch.
Serve food in trays and on tables that match with the party mood. And arrange for some competition like story telling, the spooky ones of course, and award the scariest one. Or a separate 'ghost-as-you-like' costume contest. Finally make sure that everyone leaves the place content with a fun filled heart.