Wear your number on your front!
Now other than that, no one there will know that this is your first event. Head out and have fun. As mentioned, arrive early. Bring a drink to sip on while waiting. Locat ethe porta potties and plan on using if needed about 20-30 minutes prerace.
If you have a question, ask. We all remember our first races and most runners want to see the sport continue to grow and expand. Pay attention to announcements and any signs concerning pace. Line up according to your pace.
Again as mentioned, run your race. only a few runners will actually run against competition, the rest of us are trying to run our best for the day we have.
Finally, know that all runners have some form of jitters during the pre-race. For the experienced folks, it is more hidden and more than likely not apparent to many folks. It can be something as simple as can I run xxx pace and who is here that I need to be concerned with. For a newly, well I sense you are feeling it now. In real simple terms, lay out a training schedule, train to the schedule, don't beat yourself up for a missed run and then forget about it. From there is it just one foot in front of the other.