Some of the best actors suffer the worst nerves in the wings. Just go for it, and remember, if you've got a moment where there seems to be nothing to do, you've forgotten something.
When things get tough that's the time to pull shutters down on real world thoughts. It's a difficult technique, but I can create an almost physical blackness to unwanted stimulus. Took a while to learn that.
There also has to be a very determined bloody-mindedness to show who's in charge. Command checks are just that, and be ready to do battle. When you step into that briefing room, you are already a captain. Not for one moment must you let anyone sense you feel different.
I recall having to go back to DC3s for my first command. After shiny new jets, the clattering noise and the confusion of crappy old ADFs rumbling round gave me the only 'throw in the towel' moment I can remember as I prepared for my Base and IR at AMS. Opened the taps and lumbered into the air and everything went like clockwork . . . even the VDF approach!