While still hunting, if you can see a deer before it's aware of you, drop down and put the stems of several fallen leaves between your fingers and a few in your mouth. Once that's done, start your stalk.
Sooner or later that deer will become aware of your presence and become alert. You will be downwind, so it's not able to smell you. If wearing some sort of camo, once you freeze in place, it will not see you but still it knows that some sort of movement had alerted it. With the deer keyed in on you, release a leaf and as it floats to the ground the deer will lock in on the movement of the leaf, forgetting about you.
Once it sees the leaf fall, a very natural thing that it had seen all it's life, it's satisfied that everything is cool. To that deer, it was just a leaf floating to the ground. Usually they will flick their tail and return to browsing or picking up acorns. Then continue the stalk until they noticed movement again. Just continue the process again and again until you are in bow range. It doesn't work every time but the times that it does is very rewarding.
Several time I have worked my way up to and inside of 20 yards. Once during a preseason scouting trip I showed a friend how I did this and we managed to get inside of 10 yards on a doe and fawn.
Warren