Shane,
- get a range finder to check every estimate you make
- spend more time estimating than you do shooting
- take notes on how you tend to judge certain yardages and certain targets under different conditions
- spend time estimating in the woods and in open fields
- determine how much you can overjudge or underjudge a target and still hit the 10 ring
-spend some time practicing using head yardage only (look at the animal not the ground
- stare at the same object that is exactly 30 or 40yds away every day for a couple minutes and try to imagine that object when your judging a target in competition
- give it some time,you will get better if you work at it