Replace wiper blades regularly.  It's easy to forget that wipers are a safety feature - until you end up driving in heavy rain.  An unclean or obscured windshield is a true hazard.  Driver's typically don't realize that the wipers are shot until the visibility is truly limited.  Then it can be too late, as many accidents are a result of poor visibility.  

Wiper blades have a limited life, as they perform a hazardous duty in harsh conditions.  Dirt, debris, and road grime roughen wipers, and sunlight breaks down their rubber edges.  The hot sun beating down on an unused wiper blade can cause just as much damage as regular use in the rain.  The recommended wiper replacement schedule is every six months.  Beyond visibility, it is important not to wait too long to replace a blade, as a torn wiper blade can allow the wiper arm to rub against the glass, possibly ruining the windshield.

To get the most from your existing wipers, inspect them periodically.  Lift each wiper arm off the glass and run your finger along its rubber edge.  If the rubber is rigid or chipped, you need new wipers.