#1 - Get a lawyer.

#2 - Read a book on the process and watch videos on Youtube of lawyers explaining what the SSA looks for.

There's tons of free and low cost info out there. Proving you have a psych diagnosis gets you nowhere. You have to offer evidence that it interferes with you working. Getting fired from a string of jobs helps. You have to also show that medical treatment did not make you more employable. The younger you are, the harder it is to get disability.