Here is my method and practice routine. Lets say the target is 43 yards away. I first estimate 20 yards. For me it is a yardage I can usually get right most of the time. I then start adding in 10 yard increments. So I find 30 yards, then 40 yards, and then guess that last bit of space to be 3 yards. I then come back to my original 20 yard estimate and judge in 10 yard increments back from the target to double check myself. It takes alot of time, but hey, they give you 2 minutes.

Now for the practice. It's not near as fun as practicing shooting but has to be done to get good at it. Fist you need a laser rangefinder. Go out in the woods, start picking objects like trees and bushes and take your time and estimate the distance. See how close you are with the rangefinder. Don't make it easy on yourself. Judge across ravines, downhill, uphill. I like to mix it up a bit and just judge 20 yards a while, and then I may pick two trees in the distance and estimate the yardage between them. Whatever you have a hard time with on the 3-D range is what you should work on.

I believe some people are naturals at shooting a bow but being an accurate and versatile distance estimator takes alot of practice.

Good luck!