One of the most difficult types of Social Security disability claims is that of a mental impairment. Medicine in the U.S. is materialistic, in that physical ailments and diseases or conditions that create physical evidence are typically considered more "real" than mental or psychological impairments.
The Social Security Administration does have a listing for mental disorders and looking at some of that information can be instructive, as it provides examples of symptoms or behavior that SSA is looking for when they allow a claim for a mental disorder or condition.
As is typically the case with an application for SSD benefits, medical evidence will be necessary for a successful claim. Providing documentation or medical records showing mental status examinations, psychological testing, and hospitalizations and treatment, such records will be useful for your claim.
In addition to medical records from various sources, the testimony you provide or that of friends and family may help fill out the picture of your functional ability, which with many mental disorders may vary over months or years. By providing information that covers a period years, you can demonstrate to SSA that your mental impairment was not a single or limited incident and that it impairs your ability to maintain a job and function in a work environment.
Similarly, records of your work attempts can be informative, perhaps providing specific examples of why you were unable to hold down a job, such as a difficulty completing simple tasks, evidence of limited concentration or the need for extra supervision when working on a task.
With sufficient medical evidence and work history, your claim for SSD benefits will have a greater likelihood of success in the application process.