As you are specifically mentioning riding in rain, does your bike have rim of disc brakes?
If rim brakes, after riding in rain and when bike is wet, using a rag wipe down the braking surfaces. You will clean off all the gritty gunk that collects there, a quick wipe of pads is good too--by doing this quickly after a rainy ride, it gets the abrasive stuff off your time and pads.