Bite your bottom lip and look up or make like your choking yourself to pull the skin taught. Tiny strokes at the hairs on your chin, as opposed to trying to follow the contour with a straight-through stroke. Look into the mirror closely to watch, sounds silly but it kinda helps you get used to it. You are, after all shaving hairs with a blade, as opposed to what we're used to with safety razors in running a perpendicular enclosure over skin.