Like the guys above said, practice - but learning when to take the shot is not as important as learning when NOT to take the shot. Point being, if you're not comfortable with your ability to hit, then pass up on the shot. Set your range from your stand and don't deviate - if you set 20 yards as your max, that means that you have to pass on that 22 yard shot. If you set 30 yards, then you have to pass on that 32 yard shot. You're not less of a bowhunter if you decide to let one walk because your not 99% certain in your shot.