For those of you who may be new to the game...read this man's post carefully. Pay attention....there is a lot of knowledge and good advice here.
Years ago I started doing something that I found to be very helpful in learning to track a wounded animal.
Get as clear in your mind as you can as to where the animal was when you shot. Then, even if you saw it fall and know it is dead...go to where it was standing when you shot & look for hair, blood, flesh, tracks...anything you can find. Forget that you know where it is and track it until you find it. May sound stupid, but it is a great way to get real world experience that will come in handy for those times when you do NOT see it drop.
Most of the area where I hunt is very thickly wooded with a lot of underbrush. I've been amazed more than once how hard they can be to see even within 10 yards. A dying deer will try and burrow into the thickest stuff it can find. Lastly, check out closely anything you see that is white