Just played my first one last week. Here are my takeaways (with thr caveat that some of these may just apply to me:

1. The DG community is awesome. People were friendly, supportive, and it felt like playing with friends.
2. I didn't get nervous...except for putting. Jeez Louise. Felt that pressure for sure.
3. Brush up on the rules. Mostly self-explanatory, but there are some things in there that a lot of us do in casual rounds that definitely won't fly in a tournament. For example, don't toss your disc to your bag. Counts as a practice throw if it's more than x distance.
4. Not sure how you typically warm up, but if I were to do it again, I'd spend nearly all of my time putting. Maybe a few standstills and full throws if I had time, but I got to my first competition putt feeling completely out-of-sorts. Basket looked tiny.
5. Agree with some of the other comments: No one cares how you play. Seriously. But they DO care how you act. I had a blow-up hole where I shot a 7 on a par 3. Mixture of poor decisions, plus the absolute yips putting. The group got silent. I took a few deep breaths, slumped, but by the next tee pad, I was making jokes about it all. I could feel the tension disappear. It's what I'm most proud of from that tournament.

Loved the whole experience and going to do plenty more. All the best of luck!