As well as what's mentioned previously I must recommend a damn good nights sleep if you are going to be playing in high temperature. Give the heavy drinking the night before a miss because it will make you dehydrate very easily the next day.
Always keep your fluid levels high, keep drinking water whether you feel thirsty or not, prevention is easier than the cure. Also of course, try to minimise the amount of time you spend in the sun, find shady areas but don't let yourself sit still for too long. It is imperative that you keep your muscles moving to prevent cramps, so try to avoid lounging around in the shade just before you go out to play. Also I'd recommend only wearing your full playing gear (gogs, hats, packs etc) only when you are gonna be playing, no point suffering more if you don't need to.