Use a surge protector (you don't want a power spike taking out the document you just finished, not to mention your motherboard!).
Be a computer eco-freak...dust-free, out of direct sunlight, and away from strong magnetic fields.
Check cable connections now and then. And screws too, you know the saying about "loose screws"....*g*
Don't be too power button friendly. If you're going to be away for a while, sure, then shut it off (say, longer than one or two days). On the other hand, if you step away to grab a smoke or a cold one or to walk your panting pup, leave it on, no problem.
If you live in an area that always have flashes of lightning, disconnect your phone line from your modem after you have finished using it. Modems are sensitive equipments.
