I use my index finger at the corner of my mouth. Found that using the index instead of the middle finger changed the angle of the string near my nose, which let me get the arrow under my eye without getting my nose raked by the string. That helped me be repeatable.
For good back tension, I envision (visualize) drawing the final 1/3 of the draw, and coming to anchor, using only my shoulder blade (even though it isn't a muscle).
I took a 25 year hiatus from traditional archery, so I had to relearn everything. Probably for the best. But those 2 things, just in the last 6 weeks, have helped my accuracy, consistency, and ability to shoot longer without fatigue than I could describe.