Hot-weather riding can be strenuous for motorcyclists, but it's even tougher on our bikes. High-revving engines generate lots of heat, and the full-coverage bodywork common on many modern bikes tends to retain that heat, so you should do your best to ease the strain where you can.
If you're not moving, shut off your engine. Keep in mind that WFO runs in the doggiest days of summer can lead to overheating. Never put cold water on or in a hot engine, as you can cause serious damage, possibly even cracking the block.
Check your bike's oil level, tire pressures, chain condition and coolant levels more frequently. Tires run at extreme temperatures for prolonged periods can wear much more rapidly. If you'll be riding in extreme heat for an extended time, consider running heavier-weight oil--when oil gets too hot it can't lubricate effectively. There are products available, such as Engine Ice, that can reduce your cooling system's operating temperature. If you decide to run water instead of a coolant/ water mix, add something that will lubricate your water pump--Water Wetter, for example.
Look for symptoms of vapor lock--a condition in which very hot fuel fails to flow or be drawn into the carburetors (normally not a problem with injected bikes) remedied by opening the filler cap. And be cautious about filling up to the brim in the cool of the morning. Later, especially if you allow the bike to sit in the sun, the fuel will expand and may force itself out of the over-flow system.
Riding early in the day--at dawn in really hot climates--can help keep both you and your bike cooler. When you stop for your midday meal break, take a tip from another culture and enjoy an extended siesta to avoid the hottest portion of the day. When riding at daybreak or dusk, watch out for animals on the road.
When you've got a choice of routes, take the high road, literally. Roads at higher altitudes tend to be cooler. As an added benefit, those foothill and mountain roads are also usually a lot more fun to ride. Sorry, no advice for those of you in Kansas.
Cover your seat when you're not on the bike to avoid unnecessary heat buildup. You may even want to consider using some kind of semipermanent cover in a lighter color to help prevent the dreaded butt-burn!