Once I let my nerves get the best of me during a show and the trainer I was working with let me have it! (she was not the forgiving type) But something she said really stuck with me. She said, "Don't you DARE ever let anything come in between the communication between you and your horse!!" I realized that day that that's exactly what show nerves do, they affect our relationship with our horses and affect the way we communicate with them. Practice practice practice + Time in the show ring + mental discipline. While I might get a few flashes of anxiety/excitement here and there it's been a while since I've felt true show nerves. Be prepared as you can be, train your mind to focus on nothing but the ride, and don't forget to have fun!
Also, you mentioned you've talked to several people but they're nervous too? Make sure you don't feed into each other nervousness! If you need to get away and sit by yourself to picture yourself doing the pattern successfully, do it.