This is a tip I learned a long time ago and it has worked wonders for me time and again. When a deer is approaching you and your in your stand or on the ground, typically a hunter will do what is instinctive to do, which is look at the deer. However, looking at a deer is the same as staring at a deer sometimes they never know you are there and other times they look right at you and stare back.
When this happens, never continue to stare at a deer in the eyes. A deer can sense something is wrong and if you are staring at it then it can sense this as well. Humans are the only predators to have white as the base color of their eyes and a stare down with a cautious deer can lead to a white flag and a snort! Whenever a deer looks back at you, slowly close your eyes till you can barely see it or close them all the way and wait. This can and will help you in the woods, just think about it and give it a try!