All the advice above is good except for the stuff about alcohol. I just hope they were doing it after the match. Even then they have to deal with the hangover and dehydration the next morning. Back in the 70's when some bullseye pistol shooters were still shooting "wet", an old shooter told me "Booze doesn't help your shooting, but it sure makes losing easier to take." He was only half kidding.
I recommend you get a copy of of the book "Competitive Shooting" by A.A. Yur'yev. He was a coach for the Soviets. It's available on the NRA's website in their book store. Besides detailed recommendations on shooting positions, trigger techniques, breathing control, etc., he also talks about general physical conditioning. He advises against alcohol, tobacco, and caffeine.
Another pistol shooter I know told me recently he quit chewing tobacco. He said the decrease in arm movement was dramatic. "It's like putting my arm on a bench now."
And then years ago I watched a national championship category shooter drink a cup of coffee and smoke a cigarette before the .22 pistol match. He shot a 892 out of 900 that morning. Only 8 shots leaked out into the nine ring out of 90 shots. That's 30 shots slow fire at 50 yards, 30 timed fire at 25, and 30 rapid fire at 25. All one-handed. But for us mere humans I wouldn't recommend that.
Bottom line, the cleaner your system and the better shape you are in, the better you will shoot, whether it's rifle or pistol. Then dry fire, dry fire, dry fire, practice, practice, practice.
Oh, and then do what I say, not I do. Unfortunately I don't take a lot of my own advice. But then I'm stuck in AA. It all depends on how much you want something and how much time and effort you are willing to spend on it.
Good luck with your shooting career.