Not having enough software or the right software for the lesson. Letting your kids play around with your lesson software before you teach with it. Get some game software for mess-around times. Not having a lesson plan and not being prepared. If you're not previewing, preparing and going into class with a lesson plan, let somebody else teach my kids, thanks.
Multimedia software is also more appealing to the mind's multiple learning pathways.
Hey, if you have more mistakes you'd like to caution others about, drop me some email . This list may be copied for non-commercial teaching use only.