You should view the effort to get the character or reason for your military discharge changed as a battle. The enemy is the system that discharged you. Your strategy is to choose the most appropriate arguments to make and where to make them. Your ammunition is the evidence that you submit. If you're saying that you're not guilty then you have to prove it. If you're guilty, but you think that the punishment was too harsh or the law wasn't followed in your discharge process, you have to present a detailed argument and submit evidence.
Each service has a DRB, Discharge Review Board, and a BCMR, Board for the Correction of Military/Naval Records. Each board has different application forms, rules and powers. The DD 293 is the DRB application and the BCMR uses the DD 149. You can attach as many documents as necessary and you have up to 25 pages to present your arguments. Because the BCMR doesn't allow personal hearings and the DRB's do, most veterans take their cases to the DRB first. Take advantage of this hearing, it's the most important thing that you can do to make the upgrade more likely. DRB's can change the character of discharge, the RE code and the reason for discharge, except changing the reason to “physical disability.” Only the BCMR, not the DRB, can review a discharge over 15 years old or upgrade a Bad Conduct Discharge, BCD, or Dishonorable Discharge, DD, given in a General Court Martial. Only the BCMR, not the DRB, can change the reason for discharge to physical disability, or revoke a discharge and reinstate a veteran to active duty.
You can argue that your discharge is “inequitable.” That means that it's “unfair” because it was too severe for the offenses that you committed. The Boards can determine that under “current standards” you shouldn't have been given a bad discharge. You could argue that the command didn't give enough weight to your previous good record, awards and decorations. You could argue that abuse or discrimination or that family or medical problems impaired your ability to serve.
You can argue that the discharge was “improper.” That means that they didn't follow the correct procedure when they discharged you. Perhaps they didn't do enough to “rehabilitate” you first. Perhaps you weren't given proper legal advice or were previously denied a discharge for other reasons. Perhaps the command didn't complete or process the forms correctly. Perhaps they violated rules during the Admin. Discharge Board hearing.
Start by getting your military records using the Standard Form 180 (SF 180.) Ask for “complete personnel and medical records including the case separation file and court martial transcript.” First write up your story about what happened. Next try to make a list of all evidence that proves your story is true. Go over your story and make sure that you use to all of the pieces of evidence. If you see that you need more evidence to prove critical points that you make in your story, explain why evidence is unavailable.
If medical opinions say that your Post Traumatic Stress Disorder caused the misconduct that earned you an OTH, General Discharge under Other Than Honorable conditions, or a BCD from a Special Court Martial, you may be able to get a medical discharge. Present the medical evidence to both boards. Ask the DRB for a change in character, and the BCMR for a change in reason. The same evidence can then be used to get “service connected” benefits and treatment priority from the VA.
Your odds of success improve with every document that you attach. Some Veterans Service Organizations provide help with this, but you have to look hard. Using a Discharge Upgrade manual or the “Reading Rooms” of previous BCMR or DRB decisions gets your odds above 50%. Lawyers cost but they can make the difference in difficult cases or if this is your second, or third try. We don't yet have any lawyers who are willing to help, but ask.