Between heartbeatsaround 50% exhale.

Fire as soon as you aquire target. The object is to learn tobe accuratewithout thought.
Fire from all positions possible.
Hanging upside down from a low limb is a good way to learn to fire awkward. (safety concern ? use bb repeater)
Hunt smallgame/furbearers with rifle. The best "training" I know of.
Aside from sighting inand learning wind never shoot from a bench.
Always wear full hunting gear.
Use small targets and moving targets.
Increase/Decrease shot distance/angle at random.
If you ever get a "thought" try it, what may not work for others may work for you.
Use your sling.
Use the heaviest recoiling rifle you own as much as possible but dont overdo it.