
Don't get wet?
Seriously though, I've ridden in the rain plenty of times. Be VERY careful when it first starts raining, especially if it hasn't rained in a while. There will be more oil on the road than normal for the first 30 minutes or so.. give it time to run off. Also, be extra cautious with the back brake in the rain.. same goes for when it's dry but it's doubly important in the rain.
Don't make sudden starts/stops. It's rather scary to hit the gas hard in an intersection and have your rear tire spin on you.
If the rain is steady and persistent, you should be able to ride fairly normally. Just look for pools of water to avoid.
And be extra cautious of drivers.. people do stupid things when the water starts to fall from the sky.