Reduced visibility conditions include twilight, darkness, rain, snow, fog, smoke, and bright sunshine.
Use moderation in judging safe speed. Slow down enough to maintain a safe stopping distance.
Do no slow down so much that you become a risk to drivers behind you.
Be aware that in reduced visibility conditions, drivers tend to follow the tail lights of vehicles in front of them. If you must pull off of the road, pull as far off of the road as possible, turn off your headlights, take your foot off of the brake pedal, and turn on your hazard lights.
Make sure you have a pair of sunglasses in your vehicle to deal with bright sunlight.