I hesitate to be the first to answer this since there are many more qualified to answer this, Springville shooter comes to mind.
However, for me it is the basics, your first part of your question is I do my best from a bench rest, I have a portable one that has padded leather rests but sand bags are great.
You mentioned a good trigger, the better the trigger the better I can shoot.
But for me, it is as I said, the basics.
Proper sight alignment, proper sight picture, breathing control, trigger press. "DON'T FORGET TO BREATHE"
Then perfect practice, not just practice, you don't want to practice bad habits.
Make sure the butt of the rifle is seated in to your shoulder pocket the same every time, this is kind of like making sure your anchor point in archery is the same every time.
Watch that you don't hold your breath too long, "DON'T FORGET TO BREATHE". If you find yourself starting to shake a little, relax and back off for a few moments then try again.
Don't worry about the last shot, concentrate on the shot you are making. Concentrate on the site picture and sight alignment. "DON'T FORGET TO BREATHE."
Your rifle will shoot different as the barrel gets hot, I let mine cool every few shots, I practice more for fun and hunting so the first shot on a cool barrel is important to me. I don't shoot competition except against myself.
I reload but more for fun than accuracy, I shoot a lot of factory ammo with good results.
Then there are a lot of other factors that come into play, such as matching bullet size to twist, different types of barrels and finishes, bullet coating, etc. etc. I don't get that involved, I just enjoy shooting and trying to improve my ability. I like to grab a few guns, and a lot of ammo and spend some time at the range.
Make that second to answer
