Road riding is relentless, there is a reason roadies never smile!
I disagree with that. We smile when we exceed 40mph going downhill. No, hold on - that's a grimace. I think you may have a point there
I've recently starting MTB'ing, after many years on the road. So I can give some advice from the other side of the fence.
Firstly, don't worry about grip. Road tyres have tons of grip. Well at least they do in the dry. In the wet the grip varies depending on compound and tyre pressures. Don't let the fact that the tyres are slick worry you. Some roads tyre manufacturers - Conti for example - put grip-like patterns on their winter road tyres. But these are there for cosmetic reasons. There's no mud on the roads, and the width and profile of road tyres mean that they cut through the water at most speeds. From what I've read you'll need to be travelling over 100mph for a road tyre to start aqua-planning, so there's no need for grip to clear water. As others have said - when it's wet go slow around the corners and avoid slippery drain covers and white lines.
Braking on a road bike is easy compared to a MTB. All you need to do is make sure you're going in a straight line and grab a big handful of front brake. As the roads are 'smooth' then the front wheel won't track in the same way that a MTB front wheel does in the rough terrain. So there's no need to balance the brakes. I hardly use my rear brake on my road bike. Once the front wheel is weighted - particularly when braking hard coming down a steep hill - it doesn't take much rear brake to lose the rear wheel. When you get overtaken by your rear wheel it never ends well I can pretty stop on the spot on my road bike, all with the front brake. I've never lost the front, or even had it skid.
Another valuable tip is to always descend from the drops. Firstly, it gets your weight lower. Secondly, you get more leverage on the brakes than you do from the hoods. And you go faster!
And a final tip. Never overtake another roadie before an accent. It's just too embarrassing when they re-take you half way up the hill and leave you for dead. Wait till it gets steep and you know how good at climbing they are before overtaking.
And when overtaking on the flat the trick is to get up a good head of steam in their slip-stream and then coast past sitting up on the tops, back-peddling, and commenting on what a lovely day it is for a cruise
And of course, before you hit the road - read up on the rules - http://www.velominati.com/the-rules/