1. Avoid riding over painted areas, especially when it is raining. Painted areas become very slick when wet. Try not to ride too near the centre lines of the road during rain or snow, as this area has the added danger of collecting dirt and fuel deposits from automobiles. This goes for manhole covers, as well.
2. A puddle is not always just a puddle. While it might look like a simple, shallow puddle, looks can be deceiving - until you ride over it and it turns out to be deeper than you thought. It's a good idea to avoid riding over puddles altogether.
3. Roads are layered with fuel and oil all summer long. When winter's first rain falls, it makes for an extremely slippery surface that gives much less grip than a dry road does. Even if you've ridden a stretch of road before, it could have a layer of oil that compromises tyre grip.
4. Oil isn't the only thing that can cause a slippery film on the road. Trees produce more sap during the summer - overhanging trees can get this sap on the road and winter rain mixes with it to create a slick surface. Watch out for areas that could have tree gum on them.
5. Rain is distracting, especially for pedestrians, who try to run through the rain and across the road to keep from getting wet. Pedestrians typically hunch their shoulders and keep their heads down against the rain. This means that you'll need to keep your head up and stay aware to keep from running into people trying to dart across the road.
6. Watch your speed. This seems like an obvious one, but not everyone follows it. Don't accelerate too quickly or brake too sharply. Watch your speed with heading into a bend; the centrifugal force paired with high speed could topple you before you realise what is happening. Also take care not to gear down quickly - combined with a wet road, this may cause your back tyre to lock up.
7. Be sure to keep yourself warm. Cold hands and feet don't react quickly enough to avoid dangerous situations. A good warmer kit can keep your hands and feet warm when it's cold out.
8. Take good care of your bike. The pairing of road dirt and salt can cause oxidisation. Put a bit of vaseline or grease in places that should stay dry and wax alloy rims with a good, hard wax. This will help you to avoid an outboard motor effect. While bike covers are a popular way to keep motorcycles out of the elements, these can actually build up moisture underneath. Keep your motorcycle covered in more than one way.