I also was approved on first application. I actually typed a concise one-page letter that described my disabilities, and stated that although my condition may or may not improve slightly over next twelve months because of treatments, in all regards I will be unable to perform work for next 12 months minimum. My doctor photocopied my letter onto his letterhead, and happily signed it.
Additionally, I submitted a monthly strength chart my doctor compiled, showing 12 previous months history of increasing disability.
I am 44 years old, with a career consisting of management consulting and project management. I also received benefits for my two children. It was much easier than I imagined, but it requires a supportive physician and submitting materials that prove the basic points that SSA is looking for.