For bowhunters, the only shot that really matters is the very first one. When you get right down to it, bowhunting accuracy isn't really about shooting groups; it is about shooting one arrow, the first arrow, perfectly. However, not many of us actually practice with that in mind.
Typically, we'll go out and warm up before we get serious about making good, accurate shots. The problem is, I've never had the chance to warm up before shooting at a deer. That's why I think it's important to learn what you have to do to make that first shot perfect, every time, without any warm up.
For me, the difference between the first shot and the 10th shot is just a matter of relaxation. When I shoot my first shot, my muscles are usually tight, and I'm feeling a little tense. I usually warm out of it and allow myself to relax. However, if I can make myself fully relax during the first shot, I can almost guarantee that it's going to hit in the middle. But this is really hard to do, especially when you're shooting at a big buck. It's something you just have to practice.
Now, here's what I do to practice that first shot: For a month or so before hunting season, I keep my bow out in my garage, and every time I walk by, I grab it and shoot one arrow. It may take me several days to shoot one group. These groups aren't necessarily as tight as they would be if I warmed up and shot all the arrows at one time. And not only that, the group might be somewhere other than in the middle of the target. But I sight my bow in based on the results of a series of first shots.
If you can get all your first shots to group together, especially if they group in the same place as they do when you're warmed up, you're truly ready to go hunting.