Law Dork @ Ohio State has this post on what he went through to apply for federal judge clerkships.
I don't know anything about this any more, but I know better now than I knew when I was in law school that the best thing in the world is a federal judge clerkship, especially for a district court judge. My clerkship was sort of like high school or college - a relatively short period of time, of which many, many tales have been told. A few years back, I gave a little speech about my judge, and how working for him has affected me, and I finished with these words (at the risk of quoting myself, yet again):
"The author Scott Turow in one of his lawyer books has a character, a woman, describe the relationship between a lawyer and the judge for whom he or she clerked, and she said that just as a race horse is always known by its sire and dam, the lawyer is known by his or her judge. Like that character in the book, it is my proudest heritage in the law, that I will be known always as a Judge Williams clerk."