In addition to being relaxed...BREATHE DANGIT! So many riders don't breathe! There was a young girl I used to ride with who loved jumping. Had a great little jumping pony too. Little bugger had some air under him! He started refusing fences and she just couldn't understand why. Her trainer watched her one day and figured it out. Right as she was approaching the fence she would take a deep breath in and hold it. Like she was going under water. The little pony thought she was bracing for something and threw on the brakes...hard! She had to relearn breathing while riding and took a breath a few strides from the fence and always exhaled at the break of the fence. He stopped refusing.
It sounds so basic...yet we all do it. I've ran a barrel pattern and gotten to the gate and realized I never took a breath. Not one.