Through most of the history of the United States, the Federal Circuit Court system meant that a judge and attorneys would ride through a geographical area, and sit in the local mayor's office to hear claims. A circuit judge would spend most of his time traveling; very early in the United States' history, Supreme Court Justices spent much of their time traveling in this manner.
Technically, the Federal Circuit Court System in the traditional sense (with traveling judges) was abolished shortly before World War I, as growing urbanization (and the increasing availability of automobiles) could shift the balance of travel needed so that plaintiffs could come to the judge rather than vice versa. However, the name has persisted in common usage, even though the correct term is Federal Appellate Judge.
It is important to build up a reputation for practicing law, on both the state and Federal level. It's also where you're likely to make primary network connections and friendships that will become important later on when attempting to advance in this career. Knowing the law is only half the battle in becoming a circuit court judge; knowing who applies the law is nearly as important.
It also helps if you've served on the Federal Bench at the next lower level. It's not absolutely a requirement, and several people have made the transition from state court systems to the federal one, but serving on a lower level court system greatly improves your chances of making it to the circuit court nomination process.
Understand that the confirmation process requires a two-third majority vote of the Senate to confirm you. This means that your confirmation procedure will be highly politicized. You may be nominated or confirmed based on how well your body of case rulings supports a particular political position. Sadly, the concept of "activist judge" means that merely knowing the law is not enough. How one applies it as social remedy is now of some concern, even though that is rightfully the purpose of the legislature.
If you have the right political hacks and the right background, your name is probably already on a political shortlist. If not, it's probably time to talk to your colleagues in the Federal Judiciary, and to look at caseloads that will broaden your appeal.