I've done a lot of work to answer that question.  Over the years, I've gone through many diskettes, Zip disks, tapes, CDRs, DVDRs, hard drives, and USB devices striving for order and peace of mind.  My four requirements have not been met until now.

1 - I want backup that's automatic.  Once setup, my fingers and my memory play no part.  Set it, forget it!  But I want to be able to check and see it's OK whenever the whim strikes me.
2 - I want to backup everything.  No decisions as to what's important and what's not.  No choices to make.
3 - I want backup that's historical.  If I can't find a file lost today, how about finding it in last the night's backup, or the night before, or the week before, or whenever before it was lost.
4 - I want backup that can survive.  If my laptop is stolen or if my house burns down, I want my backup safe.

So here's what I'm doing, and I recommend you do it too: