Slow down. Most fog-related traffic fatalities occur because someone was driving too fast and couldn't stop in time to avoid a collision.
Turn your lights on so others can see you. Don't turn on your high beams, which are directed higher and will just reflect light back at you.
If you leave the road, be sure to pull off completely. Turn off your driving lights and turn on your flashers so others know you're there but won't think you are driving on the road.
Think about what other drivers see when they're behind you. If you are constantly tapping your brakes, you'll likely make them nervous - and they'll be more likely to pass you.
Use your wipers and defroster to keep the windows clear.
Watch your speedometer. Fog scatters light and reduces the contrast between objects. Studies have found that the longer a driver is in fog, the faster he or she drives. Avoid falling into this dangerous trap.
Turn off the radio and turn down the heater. Listen for other cars approaching before making a turn.
Remember that other drivers have a limited sight distance and that fog makes the roads wet. Signal early, and when you use your brakes, don't stomp on them.