One thing that I find a lot of people don't take into account is the position of the spine in the arrow. I like to set up all my inserts so that my broad heads and fletches sit at the same orientation to the spine. This has made, by far, the biggest difference in grouping with my hunting arrows. My average group size at 70 yards dropped 0.85'' between the arrows with the spine orientation matched and the ones where they weren't matched.
How do you find the position of the spine in the arrow? I have heard of floating them in the bath tub, but curious how to do this.