Remove as much of the chocolate as possible using the back of a plastic spoon and a clean, dry cloth. Do not rub the stain or spread it.
Add several drops of liquid dish soap to a cup of warm water. Mix until the water is sudsy.
Blot the solution onto the stain with a clean cloth until you've removed all of the chocolate.
Sprinkle cornstarch over the stain to soak up the grease from the chocolate. This step is especially important if your tablecloth has silk in it, because this fabric will show grease spots easier.
Work the cornstarch into the stain with a clean, dry toothbrush. Let it sit on the stain for at least 10 minutes.
Brush the cornstarch off and throw it away.
Blot the stain with rubbing alcohol if the stain is still visible.
Let the tablecloth dry completely.