While slowing down and maintaining extra space margins between you and other cars is a good practice, you should find a safe place to pull over and stop if visibility is low while driving. Obstructions such as fog, heavy rain or snow can create cause visibility issues for drivers.
The other two options are also good precautions when driving, but still not the best answers. Fully defrost your windows for driving, and use the defroster anytime your visibility lessens. And finally, you should be carefully searching and scanning your surrounds as a driver to practice good defensive driving technique.