Having just started competing this year, the best advice I can give is to do your homework before you go. There are tons of places on the Internet, on this site and others, where you can learn so much about the do's and dont's of competing.
When I went to my first event this past May, I was ready for almost everything that came our way. But I learned a few things:
1. Make sure you buy good tents. Our cheap Wal-Mart tent snapped in the first hour in stiff Rhode Island winds.
2. Make friends with the teams around you quickly. If you forget something or even just have questions, established teams are a great resource. Everyone seems eager to help.
3. Do your research on turn in boxes. There are plenty of teams that put pics of their boxes up on the Internet. The pictures can give you good ideas about what your boxes should look like. Make sure you have the right lettuce and garnish.
4. Remember to have fun!