Distance can be a tough nut, especially if you don't prepare yourself for the likelihood of taking a long shot. The only clean miss I ever had on a whitetail was when I misjudged the distance by over 100 yards. Shot over his back because I thought he was about 350 yards (7" drop). In actuality he was only about 210 yards (0.5" drop). It was an open field and I was viewing over a slight rise, cutting off vision of the deer's legs. No reference points for distance and poor proportioning for size estimation. Had to aim high in the kill zone to avoid possible ground clutter on the rise. In retrospect, it was a shot I should have passed up. The fact that he was a handsome 10-pointer and light was fading fast clouded my judgment. So I lived and learned. Fortunately, so did the buck.
I hunt from permanent stands or blinds most of the time. One of the things I do in preseason is pace off in several directions and try to get landmarks for distance from my stands. I.e., "Far left shooting lane 150 yards to the mesquite log, 80 yards to the cactus bunch on the left." Or, "220 yards straight across the field to the fence, 300 to the live oak motte north along the fenceline, 400 yards to the far southwest corner. Patch of bluestem at 75 yards left, 3 gopher holes at 100 yards right." When the deer appear, I can roughly reference them to these known distances and increase the odds that I won't miscalculate too badly.
Also I spend time waiting in my stand by estimating distances to certain objects. I start with an object I think is about 10 yards away and keep moving out toward an object at a known distance by 10 yard increments. It's a great time-killer while waiting for a deer to show up. Do it enough and you start to refine your estimating skills quite a bit. I can pretty consistently judge distances to objects out to about 150 yards at about + or - 10 yards. Beyond that I try to group things into 50 yard increments and aim accordingly. At out to 300 yards this will put a flat-shooting round within a few inches of point of aim. After that things get pretty low-percentage unless you train a LOT on those distances (I don't).