If you want try for even tighter groups, here's what's worked for me.
Use a kisser button, & a string loop, and start triggering release with your middle finger. Any 'helpers' I can use to shoot better I do. And as Tazman7 said, "Arrows are expensive", so now I know my groups are tight, I usually shoot 2 arrows then go to a different aim point. Good Luck, NYD