Location, location, location: Have your CPU tucked away in a cabinet or hidden on the floor beneath your desk? Well... don't. Your system needs plenty of ventilation to keep cool—about a foot on every side, according to smartcomputing. And while the floor may seem like a relatively cool place for your CPU, it's also a breeding ground for dust and dirt, which could block your system's all-important cooling fans. Finally, keep your system in the shade—direct sunlight may brighten your mood while you're working, but it's a serious no-no for your components.
Clean out the dust: Over time, a fair amount of dust and dirt will collect inside your CPU—it's inevitable—and as I just noted above, that dust will eventually start to block the cooling fans. Beat back the dust by opening your PC's case (don’t be afraid, a simple Philips-head screwdriver should do the trick) and spraying around the wires, circuits, and cooling fans with a can of compressed air (available at any office supply store). Squeamish about opening the case? Then just spray the cooling fans themselves—it's better than nothing. Got a laptop? Spray around the cooling vents on the sides and bottom. Repeat once a week or so and you should be in good shape.

Shut down your laptop at night: Leaving your desktop running all day, every day might be fine (if not terribly green). But laptops, which tend to run hot anyway, need their beauty sleep. If it's Miller time, go ahead and shut your notebook down for the night.