Try this trick for opening stubborn jar lids: Place one rubber band around the lid, and another around the jar. With one hand, grip the jar where the rubber band encircles it; use the other hand to twist off the lid. The rubber bands provide friction, so your hands won't slip off the jar or lid.
Opening Stubborn Jars
Martha Stewart Living, October 1999
Great idea! This also works very well with a kitchen rubber glove. Another way is to put a sharp knife under the cap and twist it so that the air is released and it helps open the jar easily.