A short word about DOF (depth of field) and aperture selection.
In shooting macros and extreme telephotos, the DOF becomes very thin. Even stopping down a few stops often will not gain enough DOF to encompass the entire subject.
But what many people may not realize is that although the DOF is still relatively shallow stopped down, the look of the background (and therefore, the feel) changes dramatically. I often talk about the "smoothness" or "clean backgrounds" here on these forums. These examples can show how drastically one can alter the look to suit one's goals.
These two images taken moments apart from the same shooting distance. The background grass is about the same distance away from the subject as I am from the subject in the opposite direction. Obviously, no amount of stopping down will allow the DOF to grow to encompass the background. However, note how different the background is rendered by just 1 stop.
Just another compromise to consider. You want to make sure the subject is adequately in focus. Yet you also want the background to look a certain way.