Taking a little bit of a twist on DonL's suggestion, how about we create a firearm safety booklet? (orginal thread viewtopic.php?f=52&t=3483&p=36579#p36579)
I am thinking something along the lines of a freely available pdf file that shows many of the common things that one does at the range, and how to do them properly. Like a step by step guide with illustration and a bit of text. We already have good illustrations of the 4 rules, how about going a bit beyond that. For example one of the things that I see most new people do when they need to check their pistol for a malfunction, they simply bring it to their chest which points it at everyone on one side of them. Showing that one should rotate 90 degrees before servicing the firearm could be one page.
Suggestions for other common mistakes?