If you’re using a PC, you should check out SyncToy. It’s a free application distributed by Microsoft, and I find it useful for doing backups. It checks for changes, so it only copies stuff that needs to be copied. You configure it by selecting folder pair(s) to sync. For backups that means specifying a folder on your C drive and a backup on an external hard drive. It can be configured to ignore file deletions so if you accidentally nuke a file on your main drive, the file will still exist on the backup drive. It’s easy to use, you can set up as many folder pairs as you like, and it runs pretty quickly.

I have a pair of external hard drives, one I keep at home and one I keep in a safe deposit box. Every month I swap the drives. So I always have a full backup at home, and I have an offsite backup copy that’s no more than a month old.

This level of paranoia arose from having a HD crash. I almost lost about two weeks of invoices. I was able to recover my old data, but I learned my lesson.