My best advice for mental training is simply to create good habits, in order to build a sense of security and calm around you. Also, you could try to distance yourself emotionally from the whole situation. In my case, I just look at it objectively: We are two guys going inside a cage to work. That's it. Try to de-escalate the pressure. Take a couple of deep breaths. Don't hype things up. And stay positive, even if you're fighting for your life.