This can be difficult, but you should try to remember that the process is not objective and often can be random and chaotic. Judges do not have a common checklist and ranking system for candidates. While one judge may value law school reputation and grades above all else, another judge (even on the same court) may choose a friend of the family, a fellow Cubs fan, or the person with the best demonstrated sense of humor. The second judge even may wind up with a better clerk!
Before you start the process of applying, be willing to accept the possible result that you will not get a clerkship and the reality that such a result is not a reflection on your abilities. However, if you are not successful the first time around, but you continue to be interested in clerking, do not give up! Off-cycle opportunities often arise, and you can certainly apply for clerkships even after you graduate.