In competition, what thoughts cross through your head between the utterance, “Standby…” and “BEEP!”? 

For me?  It depends.
There are occasional times where I am trying to remember a specific fundamental to focus on, such as “press” (as in smooth trigger press), or “slow” (reminding myself to have a cadence with my shots) if I am needing to do something particular at that moment in time.  Perhaps there is something tricky to remember about a stage (such as switching from the usual “two to the body” shots to “headshot only”).

The great majority of the time at that moment, however, my mind is quiet.  The reason for that is I have done all the mental rehearsal necessary for that particular stage or series of shots.  My mind is quiet and I try to relax my shoulders.  All of the work has already been done.  My body is ready to respond in the moment with all the fundamentals (grip, stance, breathing, trigger press, sight alignment, etc.) because I’ve put hours of practice into it.  My mind is ready to respond because I’ve completed mental rehearsals of what my desired outcome looks like. 

The true trick, for me, is to rely on my training to carry me through, and get out of my own way.  When I start to stumble (figuratively, not literally), I have a tendency to talk to myself – sometimes out loud to the great amusement of the RO – things such as, “Go faster!” or “Whoops!” or “Sh*t!”  Whenever I catch myself doing this, though, I try to stop it immediately, because any energy I’m devoting to correcting myself verbally is not serving me in shooting.  Instead, if I know I just threw a bad shot, or had a strange malfunction, my preferred reaction is to keep going.  To not let it distract me from the overall sequence.
I used to play roller derby.  One of the phrases that you would hear on the bench (where the team sat) in between jams (or 2 minute periods of play) is “Old jam / new jam.”  This phrase helps reset your brain, because if you are not careful, you can start to ruminate about what you did incorrectly, or what you should have done instead, in the previous jam that you begin to lose focus on what your next job is.  It’s one thing to take what you just learned and apply it – such as, stick with your teammates, or stop faster – but it’s another to let it completely derail your focus so much so that you lose all effectiveness during the current jam because you are so focused on the “failure” of the previous jam.  So, I translate this into the shooting sport by reminding myself some variation of, “Old stage / new stage.”  Or “old target / new target,” or whatever I’m facing in competition in that particular moment in time.  Give your training a chance to take back over and influence your performance, rather than beating yourself over what you just did.  So much of performance is mental, so let your mental game be as strong as possible!

Be safe,