It is a big topic, but if you have access to a good art text, with exercises,
you can break it down into manageable chunks. Also--Crystal Video has two
great films--one on the elements and another on the principles.
My middle schoolers are on a very basic level, so I've made them two webs
to introduce the broad topics before we start. They have to do some reading
from a vocabulary sheet or textbook, and fill in words or phrases about each
element. After we've finished with each element, including lessons and work,
we do the same with the principles. If you are allowed some bulletin board
space, build a word wall so they get used to seeing the terms.