Estimating ranges while bowhunting is a necessary skill and learning to accurately estimate ranges can only be done one way...practice. One of the funnest ways to practice estimating ranges is to go stump shooting.
Get yourself some judo or rubber blunt tip heads and go stump hunting. Pick out a tree stump, estimate its' range and shoot. After an afternoon of stump shooting your range estimating skills will be greatly enhanced. It may take several trips to the woods to go stump shooting before you are proficient at range estimation but it will be a fun learning experience and if you involve a partner it can become a fun competition also.