I can't limit it to just one there were several things that made my shooting consistent and accurate.
Close up blind bale shooting with the eyes closed while focusing on nothing but a consistent, repeatable shot twenty five y years ago, didn't know what good form was then-Myself:-)
Picking a tiny spot
Alignment-Terry
Conclusion-Rod
Videoing my shooting
Re-discovering the the blind bale, I now shoot 85% of my arrows at three yards (with the eyes closed)
And contrary to apparent consensus, going back up in weight. I dropped weight and improved short term, but lost muscle tone/strength and found shooting 50# was just as hard as shooting 65# a few years before. After progressively rebuilding my strength, 65# feels like 50# did two years back.