It depends on how you are with crowds. This won't surprise you if you're used to big cons I guess... But DragonCon is huge and the event buildings can be packed.
Be prepared for severe crowding, jostling, and heat. Wear something you can breathe in, but don't mind being bumped in.
If you're a packrat like me, I know it's easier said than done --- avoid unnecessary luggage. You'll probably be starting and stopping for long stretches on your feet.
Autograph sessions: Yes. Do not be surprised by lines that fill up a couple hours before the event. Some popular ones have closed off the queue long before event time, for lack of space.
If taking pictures, try to be careful. There have been reports of incidents where security was not friendly to chance shots of/toward celebrities. Some figures may also be expecting gratuities for any pictures.
Warnings aside, can be a very amusing con!
If you're at all into movies or just want some peace, do check out the film festival. The early ones were not jam-packed last year, and they have some nifty stuff.