It helps to use floresent tape to mark the blood trail and you can then project the travel route by looking back. Look for nearest water and thick stuff. What color was the blood? I know red right? Just kidding, the actual color will say a lot where the deer was hit. Dark blood liver, bright red muscle, bubbles in the blood, lung. Was it a pass through, blood on both sides of the trail? Did the deer ever stop and form a blood pile?