Go to the range and start tuning for best arrow flight to your aiming point. Place a vertical line on your target. Shoot at 20 yards and then 40 yards. If both groups are hitting the same (vertically), then center shot is where you want it. If not, then centershot will have to be moved. Do this until you have them hitting in a vertical plane. Then put a horizontaly line on the target (electrical tape works well). Then, at 40 yards try to hit the line with each arrow in a group. Then move the nocking point (or rest if you're using brass nock points), a very small amount in one direction and note the deviation from the line from this setting. Keep doing this in both directions, until you've found the point where the best groups are. Usually it's pretty close to where the "bullet hole" setting was.

An alternative to finding the nocking point is to shoot fixed blade broadheads and adjust until they are close to the field tips in horizontal height. It's important that the broadhead arrows are identical to the field tipped arrows. For this to happen, you have to eliminate any planning imparted by a broadhead being released in the wrong direction.