Your windshield wipers should be checked every six months. Any signs of deterioration is cause for replacement. Wipers that skid across the windshield can cause wiper "chatter," a condition where the wiper blade shudders as it skids across the windshield. This is often caused by a dirty wiper blade or windshield. Cleaning both is often enough to stop the skidding.
Pull the wiper arms away from the windshield until they lock in a vertical position.
Clear away any loose debris in the wiper's path.
Spray a liberal amount of a foam-based glass cleaner (available from any auto parts store) on the windshield and the wipers.
Wipe the wipers and the windshield down with a soft, clean cloth, being careful to remove all traces of dirt, bird droppings, tree sap or other debris on the glass or the wipers. Return the wipers to their normal position against the windshield.