It really depends on what works for you! I listen to music and spend time giving my horse like a pep talk. The more you show, the easier it gets. Practicing or running through patterns A LOT to prepare also helps me with pattern classes. Know that nerves are normal! But believe in your abilities and recognize how hard you and your horse have worked to prepare. No matter how the class goes, regardless of the result, it's not going to be the end of the world. Focus on having fun with your horse. That works for me! Good luck!
I always walk my horse off a little ways before my class away from the crowd, so it's just us two and sit and scratch his neck and give him a pep talk.
Answers can vary depending on the person. For me personally, stay calm. When you get tense, your horse does too. Just relax and have fun. Don't stress over it. Another tip is trust your horse. If you don't believe in him/her, they could back off. Just take deep breaths and have fun. Hope that helped! :)