When I wrote to my doctor I had the following paragraphs
Intro (Spoke about why I want an official diagnosis and why I know I'm an aspie)
Sensory (Mentioned all sensory issues)
Thought Process (Included in here seeing things differently, good memory, live in my own mind a lot more and not dependent on others, consuming thoughts etc)
Society/Culture Clash (Spoke about problems having a normal job, not conditioned to society etc)
Social (Spoke about others being draining and needing downtime, face blindness, things like that)
Hobbies and Interests (Spoke about obsessive interests and losing sight of time and priorities, the need to have hobbies and interests to clear the anxious restlessness, routines, collecting data etc)
OCD/Anxiety/Other (Mentioned a few other traits that seemed to fit into this category more)
It came to four and a quarter pages in the end and was probably worth speaking to me for months and even then everything was much clearer so I would recommend writing everything down so the doctor can read it before you see them and they can just ask a few questions based on that rather than you having to explain everything in one session.