At night rainy roads become especially treacherous. The glare of oncoming lights, amplified by the rain on your windscreen, can cause temporary loss of visibility while substantially increasing driver fatigue. In rainy conditions pedestrians, livestock, and wildlife are extremely hard to spot and even harder to avoid. When driving through a puddle of uncertain depth, go slow. If it's deeper than the bottom of your doors, turn around and find another route.
Deep water can cause serious damage to a modern car's electrical system.
Avoid splashing pedestrians. If possible, stay off the road during heavy thunderstorms. Large flashes of lightning can temporarily blind and disorient drivers, and the accompanying high winds and heavy rain can create deadly driving conditions. This should be obvious but it also very important. People are so used to driving certain speeds on certain roads that sometimes they forget the need to slow down when inclement weather presents itself.