My 2 cents?
Get good rain gear. If you aren't wet, shivering uncontrollably, and generally miserable, you will be more relaxed and better equipped to deal with the conditions. Keep a good coat of non-abrasive wax on the face shield. All I have to do is turn my head to the side and the water blows right off. (Bonus: Makes it easier to remove bugs in dry weather.) If you normally use a tinted shield, keep a clear one, preferably a pin lock, handy for rainy days. I have a reflective vest for night riding that I will wear when it rains. Visibility is low when it rains. Do what you can to make it easier for the cagers to see you.