Assuming you are referring to driving:
There are four basic principles that drivers must follow at all times in any condition of visibility:
1. Drive at a safe speed for the conditions. This means slower when it’s raining, snowing, or foggy outside. Not only will this help you avoid accidents, but it will also give you more time to react if something does happen.
2. Increase your following distance. Again, this gives you more time to react if something happens and also makes it less likely that you’ll rear-end someone if they have to stop suddenly.
3. Use your low beam headlights when visibility is reduced. High beams can actually make it harder to see in some conditions, so stick with the lows unless you’re in an open area with no oncoming traffic.
4. Be extra aware of pedestrians, bicyclists, and motorcyclists. They’re harder to spot in low visibility conditions and may not be as visible to other drivers as well.