For some reason - no matter how much I try to slow down - my first stage at every match is always a screw up for me. Just the excitement of competing (even though I wont be anywhere close to the top) and just knowing how fun it is. After I get that first stage under my belt - I have fun from there on out.
When I first started playing USPSA, I was dumbfounded that we couldn't "warm-up" on one of the spare bays.
"Whadaya mean no warm-up shots? How in the heck am I gonna get ready to play?"
In every other sport I ever played, you had PLENTY of time to get loose, build-up a good sweat, take a few shots, smack a few heads...etc.
To my simple mind - why should this sport be any different?
Here's what I found from reading books & in practice myself.
The calming of 1st-stage jitters is found - long before the match starts - in your practice sessions.
For instance, each time you have a practice session, do an El Prez, cold.
No warm-up shots, no bill-drills, no rounds downrange prior to running the drill.
Set the targets, mark off the distance, go thru your "Make Ready" routine
just like you would in a match.
Prepare yourself mentally - JUST LIKE IT'S A MATCH.
Do this EVERY TIME you practice.
It will take some time, but after a season of this (or less),
I think you'll find the 1st-stage jitters took a hike somewhere along the way, and
your 1st-stage performance vastly improved.