I'm on a Mac and am very bad with regular backups
On a USB drive I have a clone of my Operating System partition, done with Carbon Copy Cloner. It's 6 months old, now
CCC is great because it lets me start the computer from that USB drive and actually "fix" things on the internal installation in case anything goes wrong.
I keep important media files on a separate hard drive which is connected to my WiFi router.
Because I am always low on disk space and for now, can't afford more space or better solutions, I keep as many of the most important files as will fit on a second hard drive, as well.
That's it.
I admit I am a very bad girl in this respect.
More so because I used to work in IT for 15 years.