Most general guidelines for résumés apply in the context of judicial clerkship applications. Your résumé should indicate your academic background (including honors and activities), employment experience (including, for 2L applicants, your second summer employment), publications, outside interests/activities, and any other information that might help a judge make his/her decision.
In addition, at least two separate guidelines apply specifically to judicial clerkship résumés. First, make sure that you emphasize the research, writing and analytical skills obtained through your various academic and work experiences. Second, make sure that who you are as a person comes through in your résumé. In other words, include information you might leave out of a standard résumé, such as your hometown address (if you are applying to judges in that jurisdiction) and personal interests outside of law. Because chambers are unusually intimate environments, judges care more than most employers about how you might fit in socially.