I first heard of this exercise from a Navy Seal and have since used it as a game with my kids in the backyard. First practice walking some distance in a perfectly straight line. Choose an end goal and point your feet in that direction. Practice putting one foot carefully in front of the other, with toes slightly turned in. When you think you've got it down, blindfold yourself and try to walk perfectly straight until you reach your end goal. Observe your tendency to drift to the right or left.
When you've conquered a hundred feet of distance, try something bigger and unfamiliar like a soccer or football field, or an airstrip. The Navy Seal guy I knew practiced this with miles of distance rather than feet. The point is being able to cross a lot of territory in the dark, or blindfolded, without getting lost. As you learn to walk perfectly you will notice any “imperfect” habits of your posture, form, and movements.