OP good luck with your first lesson. I know how it feels to ride an excitable horse, but the beauty of dressage is that your instructor will show you how to effectively harness that energy and bring it round to put the horse in a good, correct working mind. I'd bring the martingale (if that makes you feel better) but wait to use it. If you need, you can always put it on half way through the lesson, but just feel it out first.
Good luck, have fun!
We are not human beings having a spiritual experience. We are spiritual beings having a human experience. -Pierre Teilhard de Chardin