The first thing I would do is go to http://www.edstandards.org and see what
your state standards are for your grade level. Then, looking at those, choose
the power standards to base your curriculum design on. A power standard has 3
criteria: 1)endurance-the knowledge will last long after the class or the
test is over, 2)leverage-knowledge that is applicable in other areas, and
3)essential-knowledge that is needed for the next level of learning. I guess you can
tell, i'm taking grad classes in curriculum.... It's as good a place to start
as any, at least whatever you come up with will be in alignment with the
state. You might also contact the other art teachers in your district and get their
input, especially about what they think is essential for the students to know
when they reach their class.
Hope this is helpful!