It happens all the time: I see a post from a friend or in a forum with a desperate plea for help because someone's hard drive failed and they have no backup of their work. It's absolutely crucial that you back up your files properly, and this helpful video will give you an overview of how to do that.
Coming to you from Mango Street, this great video will run you through a proper backup strategy to ensure that you're never without your files should something catastrophic happen. The key that many people overlook is having at least one off-site backup. Having a backup hard drive is great (remember that RAID is not a backup), but if a tornado hits your home or you're robbed, it'll do no good to have all the copies of your data in one place. A lot of people store a drive at a friend's house and bring it home once a month to update, but I personally recommend (as does the video) Backblaze. It's $5 per computer per month for unlimited backup (including attached drives), and it's saved me once already. Whatever you decide, though, just make sure you always have backups in multiple locations.