Misjudging the distance to a target is the most common reason for missed shots and lost birds. Like patterning your shotgun prior to the season, learning to judge distance accurately demands regular practice. But, learning to judge distance can be a fun, offseason game.
Cut from heavy cardboard or plywood 10 to 15 life-size turkey silhouettes. In open areas and in the woods, have a partner place a silhouette at numbered stations. Distances should vary for each station. From a sitting position, jot down on paper your estimated distance from each silhouette.
Now reverse roles with your partner and compare the results. Use an electronic range finder to verify the accuracy of your estimates, then reset the silhouettes and try it again.
Regular practice may not make your range estimations perfect, but it will make you a far better judge when that gobbler comes close enough for a clean kill.