Also, when you find the blood trail and begin to pursue it, try not to disturb the trail by walking to the side of it. Sometimes if blood is scarce, you can cover upyour blood trail by walking through it.
Also, look for broken limbs, rustled leaves, slide marks from the hoofs, blood on trees and limbs, and hair if the blood is scarce. Keep your eyes well ahead of you and take your time in case you jump the deer.
Just wanted to throw that in with what Rob said.
Great post, by the way.