I think background cover is the most important thing you can have. If you're on a tree like a pole in the middle of a field, you can be 50 feet up and they're going to see you from a half mile. If that tree has leaves and branches, even if you're between the trunk and the deer, you are harder to pick out.
When you're walking through the woods after the leaves drop, pay attention to how much sky you see through the tree tops. It changes depending on how close you are to a tree.
Where I hunt, at 12 feet up, they aren't going to see me at all from more than 50 yards. Between that and 15 yards is kind of the critical range where my movement and silhouette is most likely to get picked up, so I better be careful. Inside 15, I'm at a high enough angle above them that I can move again, unless something like noise makes them look up.