My 2 cents :
1. Make sure you have additional set of brake lights at the top of your rear windshield since visibility reduces greatly in rains and the vehicle coming from behind may not be able to gauge if we have braked.Reflectors can also server their purpose.
2. There is this certain kind of rain...
when even if you put on the wipers on the full throttle,the visibility is very bad.Best is take your car off the road at a safe place,put on the hazard lights and enjoy.Remember defrosting the window panes.
3. During long run,we may have the wiper doing its job,but very important to have the defrosting done at regular intervals.A quick wipe with a dry cloth also helps.
4. Water may accumulate in the headlights.Make sure you have it cleaned/cleared.
5. Never put on the hazard lights while driving in rains,the visibility is not even 30% of the parking lights.
6. Water suddenly splashing on the wind screen from a puddle can cause temporary blurring of the screen.I hope many have experienced it.Make sure you are aware of it.
7. Drive behind the water hollow created by vehicle in front of you when driving in waterlogged roads.You don't want water loading in your exhaust.
8. Rear windshield wiper is a must,not a luxury.Atleast we can have it wiped at regular intervals.
More coming as and when it clicks...