SAFD: A couple things I would add to the great thoughts already shared.
First, go to a meetup if you can no matter how anxious you feel about it. Last year I forced myself to go to HH on Friday after skipping out for years because I was nervous about not knowing anyone. Got there and was greeted by
@Kerry1957 who quickly made me feel at ease. Because of that I also went to the pre-race meetups for HM and full. It made the time waiting to head to the corrals fly by. You will not regret giving it a shot. And for those who are veterans of the meetups, introduce yourself to someone new. It goes a long way for those of us with social anxiety.
Second, along the lines of what others have said, take what the day gives you. Rarely does the race go according to plan. Roll with it and focus on setting a PR in fun no matter what happens otherwise. I have learned the hard way that positive mental imaging can make a world of difference. In those moments that suck, find a cool costume, stop for a character you hadn’t planned on, or simply tell a runner next to you what a great job they are doing. It helps reframe a bad situation sometimes.
Finally, thank the volunteers. Many of them are there before we are in the morning and are doing it so we can have a good race. A word of thanks means a lot.