In addition to residency training, all of the certifying boards require you to submit case histories. These requirements are specific for each of the boards and candidates should contact the boards to determine the exact requirements. In my experience, gathering the case histories was the most difficult part of the process. All of the specialty boards have a requirement for clinical experience before completion of the certification process. ABPS requires four years of post-DPM clinical experience.
All boards count the years of residency training as post-DPM clinical experience.
Each board publishes deadlines for submission of applications, case histories and required fees. Stay on top of these deadlines because the boards don't make any exceptions for those who miss them. I always mailed these documents a week in advance and used certified mail with return receipt requested. In fact, I still have those receipts. The first year that I submitted case histories to the ABPS, I was unceremoniously informed that my case mix was too narrow and I did not qualify to take the exam.