Look beyond the oncoming headlight beam (not directly into it).
Reduce the illumination of the dashboard lights (eliminates glare into the eyes or onto the windshield).
After experiencing glare from an oncoming vehicle, gradually let off the gas, look to the right slightly, resume normal driving after the vehicle passes, and do not blind other drivers with your high beams.
Clean the windshield inside and out (smokers especially). Make sure the windshield washer reservoir is full and operational. Windshield wipers should be clean and free of defects.
Clean the headlights. Dirty headlights will decrease visibility by as much as 90%.