A good start is probably having a demonstrated history of life problems caused by lack of attention/focus, ideally consistently shown and starting from childhood. Complain about inability to concentrate, losing track of time easily, &c.

Of course, I assume your goal here is to get an amphetamine prescription. That's not the only treatment used for ADHD, and if you walk in complaining of ADHD symptoms and asking about Adderall you may send up some red flags. Be careful with the law here, prescription drug abuse is frowned upon.