If I had ridden today, I would have worn sandals, no socks, shorts, a polo shirt, and a rain jacket. That's exactly what I wore today, but I didn't ride. The jacket is to keep my shirt dry. The rest is fine to get wet, because it wasn't cold. If I had ridden vigorously, I would have gotten wet from sweat, because the rain jacket keeps moisture in. But that's better than wet from rain, because it would have been warmer.

In colder rain, I would probably have added layers of synthetic or wool. I would not have exposed cotton to the rain, because that gets cold.

Leave as much skin exposed as you can without getting cold. Better to let the rain run off your naked skin than to wear soaking clothing against it.

Another useful tip is to bring a change of clothes or leave it at work. Sometimes you'll feel yucky, no matter how much planning you do. Some weather doesn't have a set of ideal clothing for it.