If it's easy to do, I try to avoid riding for about 15 minutes after it starts raining. When the road first gets wet I find it slick but after all the oil and dust and whatever is lifted off the pavement it seems to be a lot better. If I can't avoid it or it starts raining while I'm already out there, then I take it easy and leave lots of room in front of me. I always take corners pretty slow in the rain - never know what's hiding under even the thinnest sheet of water...
1986 TT225 (work in progress)