First time Dragoncon Attendee...

I have only been to one other con before (Supernatural, please don't judge lol). For that one, you pre-purchase everything, including photo ops, autographs, meet and greets, etc. How does it work at Dragon con? Do you just stand in line and hope you get one? Does anyone have any advice for someone who gets anxiety in large crowds? Any info is greatly appreciated!!

EDIT: I am so incredibly grateful for all the awesome feedback and helpful tips. You are all amazing! Please feel free to keep adding info! 4 months to go!