I ride all year round, except in heavy snow, and I do the following..
If you know you're going to be travelling some distance by bike in crappy conditions, plan ahead as much as possible.
Take an extra thin layer or two in a backpack/tailpack, along with a cheapo waterproof jacket. If you get caught in freezing rain, being able to put extra layers on to keep you warm and dry could be massively advantageous.
Tell people when to expect you, and your likely route. This is particularly pertinent if riding at night, as you could have an off and no one would look for you, and in many situations no passers by may see you.
Take a small high calorie snack and keep it with your extra layers, along with a drink of water as well. If you are in the country and the mobile reception is poor, you can break down/crash with no way of contacting anyone. Being able to keep yourself fuelled and watered can make a huge difference to how you feel, as well as having a proven impact on mental sharpness.
When riding, try to be as smooth and consistent as possible. In poor weather other road users are also distracted, having a motorcycle approach at speed can cause them to flinch as you pass, or worse appear as though they have seen you when they haven't. Don't second guess them, it's not worth it.
Don't be in too much of a hurry, 9/10 you'll get to where you're going cheaper and faster than the car in front, don't feel you should cross the wet double white line on a bend just because there is no oncoming traffic, it's not a race.
Try to avoid "bulking up" too much in the cold. Firstly, thin layers are more effective, and secondly restricting movement means you are inclined to miss out safety techniques more readily as they are harder to perform. If you're warm but can't look over your shoulder, you might want to reconsider your gear choices.
Gear choice, on powerful bikes.. Choose the highest gear that isn't straining the engine. When there is less grip, anything that translates a clumsy throttle movement more quickly to the wheels can be bad news. Sure the bike will feel less responsive in 6th at 40mph, but that can be a good thing in poor conditions.
Uprate your headlight(s) to HID, I did this on my Super Blackbird and it makes a massive difference. Being able to see broken branches, blown litter, manholes etc more clearly and at greater distance allows you to plan more effectively, and therefore give yourself more time to react. If you already have epic headlights, you know exactly what I mean.
All the other stuff I can think of has been either covered in the original article, or by the posters below. ;)