Advice for Rookies at their first regional?

[Bongle]

For your pit, have something long you can put around the edges that will give it some bounds. Whether these are toolboxes, tables, or just outright fencing, it will aid against intentional or unintentional expansion from your neighbours.

Probably too late for shirt advice, but if you're attending a big regional (50+ teams), make sure your shirts are uniquely colored. In 2006, my team at GTR had flat black shirts with text, and it made it VERY difficult to find each other in the stands because many other teams also had dark shirts and the stands aren't usually lit well. We got new red ones for Atlanta and it worked nicely at keeping us together.

Bring lots and lots of buttons or other clip-on stuff. It is the currency of the pits and stands.

This was my team's biggest change with the biggest payoff in the 2006 season:
Make a checklist of pre-match things to do, with specific people assigned to make sure they get done. Before each match, have the team leader specifically ask each person if they finished their task (even if he thinks that it has already been done). Here's an example:
[ ] - Mechanical Mike changed the battery
[ ] - Programmer Pete ensured the correct version of the code is installed
[ ] - Electrical Erica made sure all the wires were tightly plugged in.
[ ] - Driver Dan put the robot through its paces
*[ ] - Motors work in the correct directions for all orientations of the drive stick
*[ ] - Arm operates through all its possible orientations
*[ ] - Pneumatics open and close as expected and with the expected pressure
*[ ] - IR Board is responsive

We implemented this because we had one regional where we had 3-4 matches with catastrophic but avoidable failures: unplugged batteries, uncharged batteries, test versions of the code that made the robot undriveable, unfilled air tanks, unplugged PWM cables. All small things that, if unchecked, end a match for a team. Assigning people to each task is important because it makes people accountable. The person named for each task is more likely to ensure it gets done if their name is written down and the team knows exactly who is to blame if their task goes undone. I know that I (as programmer that year) made very sure that the correct version of the code was loaded, even if it meant redundantly re-downloading the correct code to the robot.

[RoboMom]

http://www.firstnemo.org/resources.htm
has suggestions, like
"18 Tips for in the Pits"
"101 Things I Wish I'd Known Before My First FIRST Competition"