At "10 dumb things users do that can mess up their computers" Debra Littlejohn Shinder brings up some interesting common failings. Lets look at her list, because I have a different take.
#1: Plug into the wall without surge protection
#2: Surf the Internet without a firewall
#3: Neglect to run or update antivirus and anti-spyware programs
#4: Install and uninstall lots of programs, especially betas
#5: Keep disks full and fragmented
#6: Open all attachments
#7: Click on everything
#8: Share and share alike
#9: Pick the wrong passwords
#10: Ignore the need for a backup and recovery plan
Well, they seem interesting, but ...
The big "but" gets back to one of my favourite phrases:
Context Is Everything
Very simply, in my own context most of this is meaningless. It may well be in yours as well.