Good question bigdog02!
Hiawatha gave some excellant advise, and I will try to add some more.
Obviously, we should ALWAYS strive to take only very high percentage shots. That being said, in the rain we should go even further, if that is possible.
I hunt when I get the time. If it is a downpour, I still hunt. When it is raining, I limit my shooting range to under 20 yards. I will ONLY take a shot that offers both lungs.
When you hit a deer through both lungs, you don`t need blood to find `em. They just are not going very far.
Good luck on opening day!