You'll find the following resources clear and readable starting points for learning more about using rubrics with your own writing assignments.
Arter, J. (2000). Rubrics, scoring guides, and performance criteria: Classroom tools for assessing and improving student learning. Paper presented at the Annual Meeting of the American Educational Research Association (New Orleans, LA, April 24-28, 2000). Available from ERIC: ED 446 100
Boston, C. (Ed.) (2002). Understanding scoring rubrics: A guide for teachers. ERIC Clearinghouse on Assessment and Evaluation. ED 471 518
Crawford, C.M. (2001). Rubrics: Models of evaluation within a constructivist learning environment. Paper presented at Annual National Council of Teachers of English Spring Conference (20th, Birmingham, AL, March 29-31, 2001). Available from ERIC: ED 462 910.
Herrington, A., & Moran, C. (2001). What happens when machines read our students' writing? College English, 63(4) 480-499. (available in JStor)
Moskal, B. (2001). Scoring Rubrics Part I. What and When? ERIC/AE Digest. ERIC: ED 446 110.
Moskal, B. (2001). Scoring Rubrics Part II. How? ERIC/AE Digest. ERIC: ED 446 111.
Stevens, D. D., & Levi, A. J. (2005). Introduction to Rubrics: An assessment tool to save grading time, convey effective feedback and promote student learning. Sterling, VA: Stylus Publishing.