ditto what bob said. the trick about detail in the targets is a good one. not only looking with the eye, but with the bino as well. look at the face of targets as well. you will see the most detail there. another trick is to judge to other object than the target. i use trees or rocks behind of and in front of the target.

the rangefinder is a great tool. i shoot practice rounds, keeping a log of what i judge the target, and then range the target. at the end of a round you will see a trend, meaning you judge 2 yards short or long consistently. uphill and downhill can get a little tricky, and small targets at longer yardages can be difficult as well. practice yardage estimation equally with you bow practice. what i have found over the years is most people can shoot very well, but judge poorly. work on what you are weakest at and move up from there.