Letting a laptop rest on your thighs — or worse, sink into a cushy comforter — prevents internal heat from radiating outward and can block air intake vents. This causes overheating, a major cause of component failure in computers. Using a laptop on a less-than-flat surface can also put the hard drive at an awkward angle, which can also cause damage.
Speaking of the hard drive, don't walk around with your laptop while the hard drive is active, because its actuator arm, which skitters over the surface reading or saving data, could bump into the drive's fragile and finicky magnetic memory material. Many modern laptops have gyroscopes that shut down the hard drive when they sense movement, but that sometimes doesn't happen fast enough to prevent harm.
“A lot of people close the lid on their laptop and throw it in their case without making sure the hard drive has shut down completely,” said Chris Kramer, director of technical support for Micro Center, a chain of 23 computer with Dell laptop battery and electronics stores that has its headquarters in Hilliard, Ohio, a suburb of Columbus.
Mr. Kramer recommends manually putting a laptop in “sleep” or “hibernate” mode before closing the lid, instead of assuming that the hard drive will shut down automatically. Then wait a beat, because computers need a second or two to do the internal housekeeping necessary to obey the command.
Even then, it's a good idea to listen for the hard drive to stop spinning before moving a laptop. Also look at the computer's lights to look for an indication that the laptop is dormant. Depending on the brand of computer, the lights may be a green, amber or red, or there could be no light. In Apple computers, it's a white light pulsating in a rhythm reminiscent of the slow, steady breath of peaceful sleep.
Owners of a computer with a solid-state drive, which is standard in the MacBook Air, don't have to worry about damage from jostling. But they too, want to make sure their laptops are in sleep mode before zipping them up in carrying cases. Otherwise, the drive could remain engaged and eventually overheat the machine.
Another common user error is leaving a laptop plugged in all the time. “A lot of people use their laptops as a desktop,” said Kevin Dane, executive director of product quality and reliability for Dell, the computer manufacturer. “Leaving it plugged in all the time diminishes the battery life and degrades its performance.” Batteries, like muscles, atrophy if not exercised. Unplugging your laptop once in a while, say two to three times per week, is enough to keep the laptop battery fit.
It's also not a good idea to drain your laptop battery completely and not recharge it for extended periods.
the source: http://www.acerapple.info/good-measures-of-the-laptop-cooling/