Happy Clean-Your-Keyboard Day! Okay, I made that up, but think about it: when was the last time you did anything with your keyboard besides drop cookie crumbs on it?
Over time, all keyboards accumulate dust, crumbs, and other everyday dirt. And all it takes for, say, your J key to stop working is for something to get lodged under it.
Meanwhile, research has shown that keyboard keys can harbor infectious germs--especially if the keyboard is shared by multiple users (a common scenario in modern households).
Bottom line: give those keys a good cleaning every now and then. For starters, buy a can of compressed air. Hold the keyboard sideways over a trashcan, then blast every single nook and cranny with the nozzle. (Maybe it's just me, but I find this kind of fun.)
Next, making sure the computer's power is off, wipe down the keys with one of those antibacterial wipe. Do the same with your mouse.
That's really all there is to it. I'm not saying you have to do this once a week, but every month or two is definitely a good idea--and anytime someone in your house is sick. A little PC hygiene goes a long way.