I've handled enough of these cases to know it is about a compelling story. Not fiction, but it needs to be a sympathetic story. It is easier for a judge or other SSA officials making a decision to pay out a case where the narrative makes sense. And what needs to make sense? It needs to make sense that based on this person's ailments he or she cannot work.
How do you go about constructing this narrative? First, look for credibility. Does what the claimant says match up with what the evidence says.
Second, are the ailments ones that would make someone disabled. In particular, do the ailments, circumstances and the relevant legal standards make this person disabled? Sometimes that is obvious, and sometimes it isn't.
Are there hard and fast rules for SSD cases? Not really, but the narrative needs to be compelling or you won't win.