When a heavy fog occurs, what is the best recommendation for drivers?

The best advice for driving in fog is do not. It is preferable that you pull off the road into a rest area or truck stop until visibility is better. If you must drive, be sure to consider the following:
• Obey all fog-related warning signs.
• Slow down before you enter fog.
• Use low-beam headlights and fog lights for best visibility even in daytime, and be alert for other drivers who may have forgotten to turn on their lights.
• Turn on your 4-way emergency flashers. This will give vehicles approaching you from behind a better opportunity to notice your vehicle.
• Watch for vehicles on the side of the roadway. Seeing taillights or headlights in front of you may not be a true indication of where the road is ahead of you. The vehicle may not be on the road at all.
• Use roadside highway reflectors as guides to determine how the road may curve ahead of you.
• Listen for traffic you cannot see.
• Avoid passing other vehicles.
• Do not stop along the side of the road, unless absolutely necessary. [California Commercial Driver Handbook]