My husband was approved last year on the first try also. (His age weighed in his favor) We filled out the application online. We spent a lot of time revising it and trying to word everything as concisely as possible. DON'T RUSH. If you PM me I can give more details. Basically what helps the most is how your pain limits your ability to move. Saying you have severe pain is not enough. Saying you can't walk for more than a block, sit for more than an hour, carry anything heavier than 1 lb, etc. helps.

They will ask for medical records from every doctor you've seen going back years. It is ok to collect those records yourself and send them directly. Much better than worrying about whether someone sent them for you. You will also need letters from your primary physicians treating your RSD, surgeons etc. stating that you're disabled and how you are limited.

That's all I can think of now. Good luck!