In the interest of fairness, students should be given the criteria that will be used to grade their work before they do the work. If students know how their work will be graded, there should be fewer surprises when they receive their grades. In addition, having formal grading criteria prior to giving an assignment will make it easier for you as the instructor to grade the assignment because (1) students' work should more closely approximate the criteria you established and (2) you will know what you are looking for when you sit down to grade the work.
My collaborators and I have developed several rubrics that we use to grade APA-style writing in PSY 3001W, Introduction to Research Methods. (The W indicates that it is a "writing intensive" course with a heavy emphasis on student writing.) The rubrics we currently use are available at the web site shown below. I am providing them because members of the department have expressed an interest in sharing these resources. Feel free to use them and adapt them to your specific purposes.
The rubrics are available here: