ANSWER: Since it would be impossible to explain how to win every type of case on reconsideration, let me tell you one way that you certainly won't win. You won't win if OPM is using information about you that you are unaware of. Many applicants keep a meticulous file on their case and believe that it constitutes all of the information in their case. Many are wrong. Sometimes there are medical records that physicians not have shared with patients. Sometimes OPM obtains information from workers' compensation, from supervisors, from official personnel files, from informal agency contacts, or from other sources. You need every bit of that information and you have a right to every bit of it. You even have a right to medical information that OPM may seek to conceal from you under its "prudent physician's rule." That information is critical to you winning your case, and it should be obtained, you should go for it.
Equally important as gathering all of the factual information in your case, is designing a written argument that will make OPM change its initial decision. This requires challenging not only factual assumptions but also their legal conclusions, which are often erroneous. Most disability retirement decisions contain whole paragraphs drawn directly from previous decisions that have been stored over the years in some word processor. This is a cavalier way to adjudicate someone's rights. If you want to win, you have to turn this around.