The wiper blades come first and foremost. It might seem like you just bought them or your car is fairly new, but those thin strips of rubber deteriorate easily in the summer heat. If they're not clearing rain away, it's time to replace them.
New blades are about $20 to $50 a pair depending on your car, and they aren't hard to change. If you do need help, Pep Boys says they'll give their wiper blade customers a free installation in just a couple of minutes.
And be sure to use the fitment guide, whether it's old school or high-tech. Keep in mind that on many modern cars, the right and left blades are different lengths. Don't just measure one blade and buy two of them, or you could have problems. Washer fluid is important too: It cleans better than plain water.
Moving from the rubber on the glass to the rubber on the wheels, tire tread is critical for driving on wet roads. A professional can check your tread depth, and here's a way to do it yourself: Stick a quarter into the grooves upside down. If you can see the top of Washington's head, it's time for new tread.
It might also be time for new bulbs, so check to make sure they're all working. Driving with your headlights on while using your wipers is the law, and don't just rely on daytime running lights or automatic lights because they won't always activate all the bulbs during the day. Manually switch on the full light system whenever it's raining so you can be seen by other drivers.
You also want to be able to see out of your car. So whenever you're driving in the rain, run the defroster. It's not just for the windshield; it also keeps moisture off all the windows.