A recent article in Scientific American outlines some interesting research on how you might choke up under pressure.
The key to avoiding choking up is not to focus on all the minute details: doing so inhibits the part of your brain that is better suited to that task, and leaves you running in a slower, less responsive, and more error-prone processing mode. But on the other hand, not concentrating at all isn't the answer. That would wreck your performance too.
The key, in a Goldilocks sort of manner, is to find the degree of focus that is just right. Not too much, not too little.
This right balance seems to lie in something like a one-word mantra, such as "smooth" or "forceful." Focusing on a single keyword acts as enough of a cue to activate all the necessary mental programs, but not in so much detail that your CPU bogs down processing it all.
This reinforces the explanation in Pragmatic Thinking and Learning that describes the ski instructor yelling so many directions ("tips up! elbows in! head down!") that you get a brain freeze.
Don't overthink it.
Thanks to Linda Rising for passing this on.