No special technique - other than making sure you hold the sight pin on the target as the arrow is flying. Very tempting to lower the bow and look, since you have the better part of a whole second before the arrow gets there. Short of getting another pin, you might place some sort of aiming point about a foot above the intended point of impact, and use the 40 yard pin to shoot at 50 - see if the pin is the problem. Another issue some folks battle is that, beyond a certain distance, they can't focus on the pin very well if they are focusing on the target. One of them is going to be a blur.