It's all well and good to try to prepare, but if you plan to tell the T everything about yourself, you'll do all the talking and there won't be much of an interaction.

Maybe think about writing one 1/2 page paragraph about "what it feels like being me." It might involve your everyday difficulties, childhood experiences, family info, relationships, dreams, fears. Whatever is most at the front of your mind. Avoid diagnosing yourself; painting a picture of your experience will be more useful to your T.

Give it to the T at the session, and let the T take it from there.