Not just practice, quality practice. Learn to be accurate, to have super sharp broadheads, perfect arrow flight, a quiet shot. Learn to read the animal's body language--much less apt to "jump the string" if they are relaxed when you shoot vs. alert. Spend as much time as you can in the woods. Talk to people who know how to hunt vs. those who just know how to talk/type about it (lots of that on some sites). Get advice from people in your area--just because it's a whitetail doesn't mean it acts the same everywhere.

Good luck!

Chad