I have many first rules (some for discipline, some for teaching, some for philosophy), but I'll give you my first rule in teaching:
simply put: It's the first time for them. (This is also a performing/theater rule...in as much as your audience paid big bucks for your performance and even though you might have done it umpteen times before they deserve a fresh show).
I try to remember the magic in the lesson and bring that to the forefront when teaching...I remember for example the "aha" feeling I got when I first learned perspective, or the "ooooooohhhhs" I said when I first learned about foreground,midground or background, and was able to translate that into a weaving, or how the mystery of drawing proportioned faces was revealed to me by my art teacher.
I am not suggesting that you put on a costume and entertain the kids, but what I am saying is that we must keep the material fresh, relevant, and meaningful and connect the dots with our lessons...