and another thought
(1.) Dress for the weather. If it's warm out, always wear a hat and use sun screen. If it's cold & windy or rainy, dress in multiple layers with a breathable water resistant outer garment (I usually use a GI Gore-Tex parka). If you will be active helping RO the match or scoring targets or resetting steel or something, don't dress as heavyily and be sure you don't overheat.
(2.) At all times HYDRATE! Don't drink too much coffee or Coke or other products that may act as a diruetic (although I think you can get away with a little bit. Need that caffeine to get your motor running . . . ) Cold water works best, but electrolyte replacement drinks like Gatorade or ERG are also a good idea as part of your hydration regimen. (I like iced green or herbal tea with a little bit of honey in it during the summer). I've seen plenty of instances at matches and during training exercises where a guy's performance will suddenly deteriorate, and it's because they're starting to overheat and get dehydrated. (I particularly saw this when I was in the MPs, because we always shot wearing BDUs and helmet and LBE and usually with armor, and it was really easy to get overheated)
(3.) Don't eat too much before the match (except maybe in cold weather). The process of digestion diverts blood flow from your brain to your guts and can make you a little foggy and unfocused.
(4.) If it's a longer event, or you have to wait around for a long time, snack on something between stages. (there is a lengthy discussion on the forum on the Brian Enos website about how to eat before and during a match). I like to take an assortment of power bars, but I've also used raw carrots, bananas, and home-made trail mix with lots of dried fruit and nuts in it. This summer I saw several IPSC shooters experimenting with the energy gel type products that runners and cyclists use. I've never used them myself, and have heard that they can create a quick and massive sugar low if you aren't involved in lots of physical exertion. I always take handi-wipes to clean up with before I snack on anything.
You can only learn from experience if you pay attention!