An effective way to write characters is to show them demonstrating the traits you attribute to them--to characterize by actions. This is essentially showing, rather than telling, character traits.
Regarding the Rubric: Please be aware that in my school we do not give minus grades. So no A- or C-, etc. We do have plus grades (A+ or C+), but the plus is independent of the rubric criteria; it is something extra, something above and beyond. Most of the time it's conventions (spelling, capitalization, punctuation, grammar), as it is for this assignment.