There's an old saying that everyone should take to heart: "There are two kinds of computer users: those who have lost data and those who are about to." I belong in that first camp, but it only took one nasty experience with an accidentally-deleted term paper to force me to resolve never to let that label get applied to me again. That night long ago, when I lost the fruits of my labors analyzing the great film Raising Arizona, taught me the hard way that backup is essential.
There's another anonymous saying that is also quite true, but I'll leave it to you to parse and ponder: "There are only 10 kinds of people in the world: those who understand binary and those who do not."
Backing up your computer is key to making sure that you don't lose your valuable data when disaster strikes. Here are some things I've written that will help you back up better.
No matter what backup tool you choose, there's one little detail that I want to emphasize. It's not enough to back your data up: you also need to test your backups to verify that you can, in fact, restore your data. Don't make the mistake of some companies I've known, who operated on the "I assume" theory of backing up: "I'm going through the motions successfully, so I assume that everything is working."
Make sure your data can be recovered and that it will work as you expect. You don't need to do this every single time with every single backup, but do test it out semi-regularly. You'll be glad you did.