Professor Orin Kerr of the The George Washington University School of Law posted an essay entitled "How to Read a Judicial Opinion: A Guide for New Law Students" on his blog.

It's a must read for incoming law students because cases are assigned for the first day of class with the idea that you already know or will pick up the ability to properly read a case.

CALI has a "How to Brief a Case" lesson (found here, with the legal research lessons for learnthelaw users) that would be a nice supplement to this article. But you'll stop briefing cases at some point in your law school career. Knowing how to read a case and what to take from that case is much more important.