Start by listing the key elements you feel are most important to respond to in this assignment. (Don't use a generic rubric because you'll feel compelled to include someone else's criteria.) Eventually, these elements will become the criteria you'll list in the left-hand boxes of your table. But think carefully about these elements. Do you really need to include all of them in your assessment of this piece of writing? Might some be combined? Might some be pulled apart so that you can give students more detailed response? Don't rush through this part of the process because the more time you spend on this step and the next two, the more useful the rubric will be overall.