[Rik]

Shoot at least a few times each week. Exercise on the days you don't shoot. Keep well hydrated while shooting. Take a chair so that you can sit down between ends.

I've noticed that a lot of people shoot differently at longer distances. It's a bad thing, over all. You should shoot at all distances more or less exactly the same way you shoot at your best distance. Otherwise you'll be robbing yourself of points. The shooting doesn't (shouldn't) really change with distance.