The first thing I do when preparing to ride in the rain is put on my high viz yellow lime Aerostich suit and my Sidi on road boots. Both are lined with Goretex and extremely waterproof. I also clean the inside of my visor with Windex, which sort of helps with the fog. The basic gist of what I'm saying is wear the right gear, because it's dangerous enough out there when it's dry, let alone wet. And don't say anything about me being a rich bastard, I bought all this stuff with plastic. I couldn't afford not to.
The next thing I do before I start my BMW GS 1150 is turn the ABS on. Actually, it's always on, so I don't turn it off, like I usually do when it's dry. It works, as I have found out several times during heavy braking in the rain. Besides that, I definitely keep the shenanigans to a minimum, paying more attention to making sure car drivers can see me. OK, I will powerslide around a corner or two.
With the right gear, rain never has to be a reason not to ride.