I have never presented at a National, but have at my local conference and wanted to give my perspective on WHAT NOT TO DO.
1. Take pictures without permission. You should always ask the presenter if they mind if you take pictures. Common courtesy dictates that these workshops are the presenters' intellectual property, and perhaps they don't want you to take pictures. I never minded, but one can never tell.
2. Ask for handouts but not stay for the workshop. If the workshops are ticketed, the presenters only have x amount of handouts/packages of materials. Every year I have teachers come up and ask if I have any extra materials that they can have because they can't stay for the workshop (fill in the blank for the reasons why). As an aside, I always marveled at teachers who wanted to know where the lesson plans were in the materials I handed out. I always figured that teachers would write their own lesson plans and tailor them to their own students, so I never included lesson plans. Just like I teach my students not to lift imagery, I would hope art teachers could take what they learned and customize it.
3. Start making/reading etc, before the presenter is finished with their presentation. Keeping in mind that the presenter is essentially a teacher in a foreign room, with a room full of students they don't know, let them guide you through the project at the pace they have worked out. Timing is everything, and if you get ahead of everyone else, it might throw everything off.
4. Take more stuff than your allotted materials. If materials are laid out in buffet style, be courteous and realize you do have to share materials. Everyone is anxious to get "their share", so please remember that there is a room full of your colleagues as eager as you are.
5. Monopolize the presenter. Usually there is only one presenter, and that presenter has to move around the room, just like a classroom. Remember the kid in your room that gets all of your attention? Don't be that kid.
Sorry to be a wet blanket, but just wanted to give you a heads up.