Daily Backups Are Your Friend
Absolutely nothing matches the sick feeling in the pit of your stomach when you realize that all the work you've done for the last six months has been lost due to a hardware fault that destroyed all the data on the disk. If you're lucky, you might get some relief by finding a few older versions of files on your laptop or on a long-forgotten floppy, but that's a small consolation for losing months of work.
Every day, without fail, save all of your valuable, project-specific files to permanent, offline media.
You only have to back up the valuable files. Anything you don't bother to back up is by definition not valuable, since by not backing it up you're stating that it doesn't matter if you lose it.
Keep the backups for each project separate. Keeping your projects separate ensures that you can always re-create an entire project from a single backup image. It's a real waste of time to have to restore from several different backup images in order to re-create a single project.
Periodically restore from the backupsto prove that you can. Make sure that you can use your baseline image on a new machine and restore your project from the backups. Practice this every month or so. It's extremely embarrassing to discover that the backups haven't worked for the past six months.
Keep some old versions of the backups. You never know when you'll discover that the file you deleted a year ago was actually needed. The price of the storage space is cheap compared to the cost of re-creating old files.
Keep the backups in offline storage. After all, you never know when some malicious software will get through the firewall to erase or damage all of your files.
Keep the backups for really valuable projects in a fireproof safe. Sometimes a little bit of paranoia is a healthy thing.
Keep copies of backups for very valuable projects in an offsite fireproof safe. Every week or so, take a copy of the current backup and store it offsite, just in case your paranoia was justified.