You do not have to be at the top of your class to obtain a clerkship. History has shown that Cornell Law School graduates in every quartile of the class have obtained federal and state court clerkships.
However, you do have to be realistic about your chances. You need to assess your credentials, think about your geographic location, and the likely level of competition for the clerkships you desire. Note that some judges have very individualistic criteria, such as a preference for clerks who went to their alma mater or who will remain to practice in the community.
Between the time that you apply and the time that a judge considers your application, many months may pass. Whenever you receive new grades or wish to share a major accomplishment (like winning a moot court competition or having a note published), be sure to update all of the judges to whom you’ve applied. You can send judges updates by uploading new materials to a finalized application on OSCAR or by sending the judge a short, professional letter. This will provide the judge with useful information, evidence your continued interest in the position, and demonstrate your professionalism.