Dirt on your windshield can make sun glare much worse, so keep your windshield clean.
But Consumer Reports says don't use high-gloss vinyl cleaners on your dash, a shinier dash worsens the glare.
Consumer Reports says turning on your headlights is another way to fight sun glare. It won't help you, but other drivers will be able to see you better despite the sun the their eyes.
And finally, when the sun's hitting you the wrong way, you want to back off! Leave plenty of room between you and the car in front of you in case you have to stop suddenly.