When sighting in a gun or bow, it is imperative to remove as much human influence from the shot as possible. Sighting-in is not practice - it is a process to get your equipment shooting dead-on.
Gun hunters: use the best supports you can get your hands on. Sand bags or manufactured shooting rests are the best. For the ideal setup, touch the rifle as little as possible - your shoulder and trigger finger are all that are really necessary. Make sure that nothing touches the barrel itself; your sandbags should be placed under the fore-end and not the barrel itself.
Bow hunters can't remove themselves from the sighting-in equation nearly as well as gun hunters, so archers should concentrate on good form. Go through a strict mental checklist to make sure everything is in order and done the same way for each shot.
Both archers and gun hunters should start sighting in at short distances. Twenty-five yards for guns and 5 to 10 yards for bows is not too close. Many hunters make the mistake of moving back as soon as their shot is "on the paper." Take advantage of the short distance to really fine-tune your shot. You can make almost all your adjustments at short range. In fact, both bow shooters and gun hunters can sight in at about 1-inch high at short range and be dead on at hunting distances.
Practice, on the other hand, is repeating proper technique over and over to make it natural. Where the shot hits is not as important in practice as the form of the shooter. All your emphasis and attention should be on what you are doing and not what the equipment is doing.
The bottom line: sight in your equipment to make practice more enjoyable, but try not to mix the two.