Back up your computer files often and always. And then make back ups of those back ups. And then, when you start hearing that clicking sound--that sound that is not unlike if a grossy bug was inside your computer--to get it checked out (and backed up some more) right away because soon it will be dead due to a crashed hard drive and with it years of photos and important (yet embarrassing now) emails and papers and chat logs.
What about you guys? Tell us what advice you wish you'd be told years ago.